Battery Charge Time Calculator
Use our battery charge time calculator to easily estimate how long it’ll take to fully charge your battery.
Battery Charge Time Calculator
Tip: If you’re solar charging your battery, you can estimate its charge time much more accurately with our solar battery charge time calculator.
How to Use This Calculator
Enter your battery capacity and select its units from the list. The unit options are milliamp hours (mAh), amp hours (Ah), watt hours (Wh), and kilowatt hours (kWh).
Enter your battery charger’s charge current and select its units from the list. The unit options are milliamps (mA), amps (A), and watts (W).
If the calculator asks for it, enter your battery voltage or charge voltage. Depending on the combination of units you selected for your battery capacity and charge current, the calculator may ask you to input a voltage.
Select your battery type from the list.
Optional: Enter your battery state of charge as a percentage. For instance, if your battery is 20% charged, you’d enter the number 20. If your battery is dead, you’d enter 0.
Click Calculate Charge Time to get your results.
Battery Charging Time Calculation Formulas
For those interested in the underlying math, here are 3 formulas to for calculating battery charging time. I start with the simplest and least accurate formula and end with the most complex but most accurate.
Formula 1
Formula: charge time = battery capacity ÷ charge current
Accuracy: Lowest
Complexity: Lowest
The easiest but least accurate way to estimate charge time is to divide battery capacity by charge current.
Most often, your battery’s capacity will be given in amp hours (Ah), and your charger’s charge current will be given in amps (A). So you’ll often see this formula written with these units:
charge time = battery capacity (Ah) ÷ charge current (A)
However, battery capacity can also be expressed in milliamp hours (mAh), watt hours (Wh) and kilowatt hours (kWh). And your battery charger may tell you its power output in milliamps (mA) or watts (W) rather than amps. So you may also see the formula written with different unit combinations.
charge time = battery capacity (mAh) ÷ charge current (mA) charge time = battery capacity (Wh) ÷ charge rate (W)
And sometimes, your units are mismatched. Your battery capacity may be given in watt hours and your charge rate in amps. Or they may be given in milliamp hours and watts.
In these cases, you need to convert the units until you have a ‘matching’ pair.- such as amp hours and amps, watt hours and watts, or milliamp hours and milliamps.
For reference, here are the formulas you need to convert between the most common units for battery capacity and charge rate. Most of them link to our relevant conversion calculator.
Battery capacity unit conversions:
- watt hours = amp hours × volts
- amp hours = watt hours ÷ volts
- milliamp hours = amp hours × 1000
- amp hours = milliamp hours ÷ 1000
- watt hours = milliamp hours × volts ÷ 1000
- milliamp hours = watt hours ÷ volts × 1000
- kilowatt hours = amp hours × volts ÷ 1000
- amp hours = kilowatt hours ÷ volts × 1000
- watt hours = kilowatt hours × 1000
- kilowatt hours = watt hours ÷ 1000
Charge rate unit conversions:
The formula itself is simple, but taking into account all the possible conversions can get a little overwhelming. So let’s run through a few examples.
Example 1: Battery Capacity in Amp Hours, Charging Current in Amps
Let’s say you have the following setup:
- Battery capacity: 100 amp hours
- Charging current: 10 amps
To calculate charging time using this formula, you simply divide battery capacity by charging current.
In this scenario, your estimated charge time is 10 hours.
Example 2: Battery Capacity in Watt Hours, Charging Rate in Watts
Let’s now consider this scenario:
Because your units are again ‘matching’, to calculate charging time you again simply divide battery capacity by charging rate.
In this scenario, your estimated charge time is 8 hours.
Example 3: Battery Capacity in Milliamp Hours, Charging Rate in Watts
Let’s consider the following scenario where the units are mismatched.
First, you need to decide which set of matching units you want to convert to. You consider watt hours for battery capacity and watts for charge rate. But you’re unable to find the battery’s voltage, which you need to convert milliamp hours to watt hours.
You know the charger’s output voltage is 5 volts, so you settle on amp hours for battery capacity and amps for charge rate.
With that decided, you first divide watts by volts to get your charging current in amps.
Next, you convert battery capacity from milliamp hours to amp hours by dividing milliamp hours by 1000.
Now you have your battery capacity and charging current in ‘matching’ units. Finally, you divide battery capacity by charging current to get charge time.
In this example, your estimated battery charging time is 1.5 hours.
Formula 2
Formula: charge time = battery capacity ÷ (charge current × charge efficiency)
Accuracy: Medium
Complexity: Medium
No battery charges and discharges with 100% efficiency. Some of the energy will be lost due to inefficiencies during the charging process.
This formula builds on the previous one by factoring in charge/discharge efficiency, which differs based on battery type.
Here are efficiency ranges of the main types of rechargeable batteries (source):
Note: Real-world charge efficiency is not fixed and varies throughout the charging process based on a number of factors, including charge rate and battery state of charge. The faster the charge, typically the less efficient it is.
Example 1: Lead Acid Battery
Let’s assume you have the following setup:
To calculate charging time using Formula 2, first you must pick a charge efficiency value for your battery. Lead acid batteries typically have energy efficiencies of around 80-85%. You’re charging your battery at 0.1C rate, which isn’t that fast, so you assume the efficiency will be around 85%.
With an efficiency percentage picked, you just need to plug the values in to the formula.
100Ah ÷ (10A × 85%) = 100Ah ÷ 8.5A = 11.76 hrs
In this example, your estimated charge time is 11.76 hours.
Recall, that, using Formula 1, we estimated the charge time for this setup to be 10 hours. Just by taking into account charge efficiency our time estimate increased by nearly 2 hours.
Example 2: LiFePO4 Battery
Let’s assume you again have the following setup:
Based on your battery being a lithium battery and the charge rate being relatively slow, you assume a charge efficiency of 95%. With that, you can plug your values into Formula 2.
1200Wh ÷ (150W × 95%) = 1200Wh ÷ 142.5W = 8.42 hrs
In this example, your estimated charge time is 8.42 hours.
Using Formula 1, we estimated this same setup to have a charge time of 8 hours. Because lithium batteries are more efficient, factoring in charge efficiency doesn’t affect our estimate as much as it did with a lead acid battery.
Example 3: Lithium Ion Battery
Again, let’s revisit the same setup as before:
First, you need to assume a charge efficiency. Based on the battery being a lithium battery and the charge rate being relatively fast, you assume the charge efficiency is 90%.
As before, you need to ‘match’ units, so you first convert the charging current to amps.
Then you convert the battery’s capacity from milliamp hours to amp hours.
With similar units, you can now plug everything into the formula to calculate charge time.
3Ah ÷ (2A × 90%) = 3Ah ÷ 1.8A = 1.67 hours
In this example, your estimated charge time is 1.67 hours.
Formula 3
Formula: charge time = (battery capacity × depth of discharge) ÷ (charge current × charge efficiency)
Accuracy: Highest
Complexity: Highest
The 2 formulas above assume that your battery is completely dead. In technical terms, this is expressed by saying the battery is at 100% depth of discharge (DoD). You can also describe it as 0% state of charge (SoC).
Formula 3 incorporates DoD to let you estimate charging time regardless of how charged your battery is.
Example 1: 50% DoD
Let’s revisit this setup, but this time assume our lead acid battery has a 50% DoD. (Most lead acid batteries should only be discharged to 50% at most to preserve battery life.)
As before, let’s assume a charging efficiency of 85%.
We have all the info we need, so we just plug the numbers into Formula 3.
(100Ah × 50%) ÷ (10A × 85%) = 50Ah ÷ 8.5A = 5.88 hrs
In this example, your battery’s estimated charge time is 5.88 hours.
Example 2: 80% DoD
For this example, imagine you have the following setup:
As before, we’ll assume that the charging efficiency is 95%.
With that in mind, here’s the calculation you’d do to calculate charge time.
(1200Wh × 80%) ÷ (150W × 95%) = 960Wh ÷ 142.5W = 6.74 hrs
In this example, it will take about 6.7 hours to fully charge your battery from 80% DoD.
Example 3: 95% DoD
Let’s say your phone battery is at 5%, meaning it’s at a 95% depth of discharge. And your phone battery and charger have the following specs:
As before, we need to convert capacity and charge rate to similar units. Let’s first convert battery capacity to amp hours.
Next, let’s convert charge current to amps.
Because the charge C-rate is relatively high, we’ll again assume a charging efficiency of 90% and then plug everything into Formula 3.
(3Ah × 95%) ÷ (2A × 90%) = 2.85Ah ÷ 1.8A = 1.58 hrs
Your phone battery will take about 1.6 hours to charge from 5% to full.
Why None of These Formulas Is Perfectly Accurate
None of these battery charge time formulas captures the real-life complexity of battery charging. Here are some more factors that affect charging time:
- Your battery may be powering something. If it is, some of the charge current will be siphoned off to continue powering that device. The more power the device is using, the longer it will take for your battery to charge fully.
- Battery chargers aren’t always outputting their max charge rate. Many battery chargers employ charging algorithms that adjust the charging current and voltage based on how charged the battery is. For example, some battery chargers slow the charge rate down drastically once the battery reaches around 70-80% charged. These charging algorithms vary based on charger and battery type.
- Batteries lose capacity as they age. An older battery will have less capacity than an identical new battery. Your 100Ah LiFePO4 battery may have only have around 85Ah capacity after 1000 cycles. And the rates at which batteries age depend on a number of factors.
- Lithium batteries have a Battery Management System (BMS). Besides consuming a modest amount of power, the BMS can adjust the charging current to protect the battery and optimize its lifespan. iPhones have a feature called Optimized Battery Charging that delays charging the phone’s battery past 80% until you need to use it.
- Lead acid battery chargers usually have a timed absorption stage. After being charged to around 70-80%, many lead acid battery chargers (and solar charge controllers) enter a timed absorption stage for the remainder of the charge cycle that is necessary for the health of the battery. It’s usually a fixed 2-3 hours, regardless of how big your battery is, or how fast your charger.
In short, batteries are wildly complex, and accurately calculating battery charge time is no easy task. It goes without saying that any charge time you calculate using the above formulas.- or our battery charge time calculator.- should be viewed as an estimate.
How Long Does it Take to Charge a Car Battery?
You are in a hurry on the way to work, and you jump into your car and quickly turn the key, but nothing happens.
The car battery is drained. You have a car battery charger in your garage, but how long does it take to charge a car battery?
Charging a car battery is not always as easy as it sounds; there are several tricks out there to save your battery and give it a longer lifetime!
In this article, you will get all the answers you want for this question, and a bit more!
How Long Does It Take to Charge a Dead Car Battery?
Generally, it takes about 2 to 4 hours to fully charge a normal-sized car battery with a 20 Amp battery charger and about 12 to 24 hours with a 4 Amp charger. The charging time heavily depends on the car battery size and the charger’s power output.
The most common rate for car battery chargers is around 4 amps. To fully charge a battery of the size 52 Ah would take about 10 hours from dead to fully loaded, but you could probably start your car within 1 hour.
First, you have to look at your car battery charger to find out how much ampere it’s giving out. High amperes charge your car battery faster. Low ampere is better for maintenance charging of your battery over long periods.
You also have to look at the size of your car battery and the battery type. Usually, a mid-sized car uses a battery of the size 40-80Ah. You also have to take in mind the kind of car battery. An AGM/GEL battery can charge up a bit faster than a regular wet battery.
Charging times with different battery chargers
Different car battery chargers give different amounts of power, so the charging time of a car battery will depend a lot on this. For sure, it takes a different amount of time to charge different types and sizes of batteries also, but there are times for a normal-sized car battery around 62 Ah.
Here is how long it takes to charge a car battery:
- 2 Amp charger: 24 to 48 hours
- 4 Amp charger: 12 to 24 hours
- 10 Amp charger: 3 to 6 hours
- 20 Amp charger: 2 to 4 hours
- 40 Amp charger: 30 minuter to 1 hour
What is the best speed to charge a car battery?
The amount of time it takes to charge your car battery should depend on what you want to acquire. Fast charging can damage your battery and will make its life shorter. Long-time charging with low amps is best for keeping the battery’s lifetime long.
Usually, a standard car battery charger is giving out 4-15 amperes. 2-4 amperes is typical for maintenance charging, and it will take around 24 hours to fully charge a dead battery at this load. Check your car battery charger for any settings for the charging rate and apply the charging rate for your needs.
To charge your car battery quickly without damaging your car battery, I would recommend charging your battery at the rate of 8-15 amperes. Charging your battery over 15 amperes can damage your battery if you are unlucky and make the lifetime shorter.
What causes a battery to go flat?
There could be many reasons why your car battery went flat. The most common reason is that you forgot a light or something similar in the car before leaving it. It can also be a problem with some electrical function that does not want to switch off when you turn off the ignition.
Also, a bad car battery can cause your battery to drain. To learn more about the different causes, you can see our article about the main reasons why your car battery is flat.
How long does a car have to run to charge a dead battery?
If you jump-start, you can also let your car’s alternator charge the car battery for you. How long it will take for your car to charge the battery depends a lot on the car engine and the size of the car battery. Cars have very different effects on the alternators, giving everything from 30 to 150 amperes.
The engine’s RPM also matters when charging a car battery, because the alternator is charging harder when it is spinning faster. If you want to charge your car battery fully with your alternator, you can expect it to take some hours.
It is always recommended to charge your dead car battery with a car battery charger instead of the engine though.
Which car battery charger is best to use?
First, you have to figure out what type of battery charger you need. Maybe you need a fast one or just a maintenance charger?
Modern chargers are easy to connect and have battery charging monitoring, which will regulate the amps themselves, but you should still check to see how many amps it’s charging with before buying one.
Cheaper chargers often promise more amps than they charge with. It’s better to choose a quality charger that gives lower amps instead. It will save your car battery, and it will minimize the risk of damage to your vehicle.
A car battery charger I really can recommend is the CTEK charger. You can find them here on our list of “Best Car Battery Chargers.” They have several sizes of their chargers for your needs, and it’s a well-known brand probably making the best car battery chargers on the market.
LiTime (aka Ampere Time) 12-Volt 100Amp-hour LiFePO4 battery review – Packs a parcel of power!
REVIEW – I have many power-hungry gadgets that gobble up power like Santa eats cookies. Keeping them running longer has always been fun! LiTime’s LiFePO4 100Ah battery is a beast that brings a sleighful of juice to my army of electronics!
What is it?
The LiTime 100Ah battery is a 12-volt lithium iron phosphate cell capable of being recharged thousands of times and used for providing power to portable electronics.
What’s in the box?
- Operating guide
- Company brochure
- Products brochure
- Product Manual
Design and features
LiFePO4 (Lithium Iron Phosphate) batteries are a relatively new technology, having only been around since the ‘90s. Lower internal resistance, more tolerance to complete charge cycles, and higher capacities than traditional cells have made them a strong choice for off-grid. storage, RV power, and solar backup.
battery’s box is sturdy enough to survive Christmas Time shipping.
The packaging is good. Foam protects the battery from making contact with the box.
The terminals have caps to prevent any chance of short-circuiting while being transported.
Documentation is in the bag…
The manual is very well-written, informative, and instructive.
Please use lots of caution when handling batteries. They pack a serious amount of punch.
Terminal bolts are provided in a bag on top of the packaging foam. Don’t lose them or mistakenly toss them.
The contact bolt threads are machined well and didn’t bind in the least when tightening them down. LiTime provides two sets.
A handy-dandy strap supports the weight of the battery for carrying and installation. This battery weighs in at a touch less than 25 pounds – considerably less than a lead-acid battery of similar size.
The construction is superb.
LiTime recommends a charge before the maiden voyage. I used a 10-Amp charger I already own. The battery was partially charged so completion was done in about 4 hours. At my charger’s 10 Amp capacity, from exhausted to full took a little more than 10-1/2 hours. The manual states that a 50 Amp charge will have the battery at full in about two hours.
The LiTime has a button on the top that enables the battery and change modes and, unlike other batteries, can turn off the battery completely. The LED in the switch flashes green during power up or if the capacity is low, solid green during normal operation (standby, charging, discharging). A solid red LED indicates the battery has activated the under-voltage protection circuit or is in the middle of the power-down sequence. Flashing red indicates a fault with the battery or BMS (battery management system).
The onboard Battery Management System is excellent. It prevents the battery from charging if the temperature falls below freezing. LiFePO4 batteries can be discharged at temperatures as low as.4°F(-20°C), but it is not recommended to charge them when it’s too cold because it will cause internal lithium plating and permanently reduce the capacity. Should this happen, the LiTime’s switch LED turns orange until the temperature rises high enough to resume charging. Still, in an emergency charging as low as 5°F(-15°C) is possible (though not recommended) by double-pressing the button. For its protection, the battery won’t accept a charge at all if the temperature is below the lower limit (and that’s a good thing).
The nominal voltage was 13.2 volts.
I ran the 100Ah battery through a sequence of tests with some impressive results. Attached to a 400-watt inverter and drawing just under 22 amps, I was able to operate a food dehydrator for over five hours. This means the battery provided about 110 Amp-hours! Bravo, LiTime!
Oh, and before you ask, that’s tea in the dehydrator.
At this rate, a 17-watt LED lightbulb drawing 0.15 amps would last over 600 hours. From their literature, a fully charged LiTime 100Ah battery is capable of charging a 60Wh laptop 21 times, a 90W portable refrigerator for over 14 hours, or a 1150W electric drill for 66 minutes. A 1000W microwave can heat leftovers for an hour and 15 minutes and a 500-watt blender can operate for 2.5 continuous hours – that’s a ton of snow cones (or margaritas if that’s your thing) on a hot summer day. For perspective, I’ve switched from AGM (advanced glass mat) to LiFePO4 in my Ryobi RM480e electric riding lawn mower and more than doubled my usable run time. Now I can vacuum the leaves from my lawn and four of my neighbors before needing to recharge! Fabulous!
As much as I’m tempted to use this battery in my car, LiTime does not recommend using them for engine starting. I would think that the 300 to 500 Amp surge current would be enough for my little l car (I previously measured my starter cranking current during summer temperatures at 130 Amps), but it gets too cold in upstate NY and I don’t want to risk damaging the battery.
I ran the battery through various exercises and it performed MUCH better than another brand of LiFEPO4 batteries I have. Build quality is outstanding, capacity is impressive, and the battery management system works flawlessly.
What I would change
Final thoughts
Are they more expensive than conventional lead-acid batteries? It depends on how you look at it – The LiTime batteries have more usable capacity, can be charged up to 4000 times (far more than about 700 full charges for an AGM), and should last about 10 years (vs. three to five for AGM). Their higher up-front cost should be easily recovered over the lifespan of the battery. The Ampere Time 100aH battery’s built-in management system, capacity, and utility are a solid choice for power, provided your charging needs keep it above freezing. Wonderful! Thanks, Ampere Time!
Price: 489.99 Where to buy: LiTime (save 3% with code: thegadgeteer ) and also available on Amazon Source: The sample for this review was supplied by LiTime.
Review: Redodo 12V 100Ah LiFePO4 Battery
USE CODE: CHARGERH FOR 3% OFF AT RedodoPower.com
Deep cycle Lithium Iron Phosphate (LiFePO4) batteries are a great alternative to power stations because, for the most part, they cost less in terms of the capacity you’re getting. You’ll still be spending less, even adding on the cost of an inverter and a battery charger. There are also ways to use these types of deep-cycle batteries without an inverter and have a direct connection to what you want to power.
I‘m looking at this Redodo 12V 100Ah LiFePO4 battery in this review. This comes from a well-known brand on Amazon, and their batteries are on the lower price side. I have done a full video review of this battery, but if you want to read a review article and take a look at photos, this one is for you.
What comes in the Box
What you’re getting in the box with this Redodo 12V 100Ah battery are four post bolts, two positive and negative insulated covers, a manual, and a piece of paper that gives you some info about the dos and don’t for the battery. You do not get a battery charger in the box and have to purchase that separately, and that’s not a problem in this case because, in general, batteries like this don’t come with battery chargers in the first place.
Overall, what you’re getting with this Redodo battery is standard for these batteries, and it’s not missing anything vital. Including four post bolts is a great addition; the manual contains rich information, and the paper giving vital info is a nice touch.
Power Capacity
So to get the Watt Hour (Wh) capacity of this Redodo battery, you have to multiply 12V and 100Ah, and you end up with a 1280Wh capacity. So, yes, this Redodo battery does have a 1280Wh capacity, and that’s a lot of power; when you consider a power station with a 1280Wh capacity, you’re looking to spend about 1,000 or more, in this case, you’re spending way less. Go ahead and look at their product page for this battery to see how little you’d pay to get so much capacity.
Of course, with a power station, you get everything already put together and ready to use. Still, as I mentioned, you can choose your inverter and battery charger when you go with a battery like this, which is very low cost. Also, this is a LiFePO4 battery, which can last for about 4,000 charge cycles. LiFePO4 batteries are the way to go because you’re getting your money’s worth, as the battery will last much longer than Lead Acid batteries or regular Lithium-Ion batteries. You’re looking at many years of usage for this Redodo battery.
Also, when it comes to powering appliances for a 1280Wh capacity, you can power a 1W appliance for 1,280 hours or a 1280W appliance for 1 hour. So you have a lot more flexibility when it comes to the longevity of the capacity depending on what appliances you’re looking to power.
MakerHawk Battery Capacity Test
For the capacity test, I used a MakerHawk load test and connected the positive and negative clamps of the load test to the Redodo battery. I set the Voltage to about 12.8V and had the Amps set to about 10 Amps. I ran this test overnight to drain the capacity of this Redodo battery to 0%. After about 9 hours, I returned to the load tester turned off, and the battery was fully depleted of its capacity. What I ended up with was a 103Ah capacity and a 1,298Wh capacity. So on the Amp Hour (Ah) reading, I got a 103% efficiency rating, and on the Watt Hour (Wh) side, I got 101% efficiency. So this Redodo 100Ah battery has a 1280Wh capacity and a bit more, so you’re spending your money wisely for not only the capacity but also the many change cycles that come with a LiFePO4 type of battery.
Also, somebody mentioned in one of my battery capacity test videos that these batteries have a bit more capacity than they say they do to ensure they output the advertised capacity.
Output Charging:
Since this battery has a 1280Wh capacity, it has a 1280W continuous power output and a 1280W max input.
For our testing of this Redodo 100Ah battery, I used a Renogy 2000W Pure Sine Wave inverter. To clarify, you don’t have to use a 2000W inverter for this Redodo battery; in fact, using this inverter is way over the top. Instead, I would recommend a 1200W inverter or lower, depending on your budget and needs; however, in this case, I wanted to push this Redodo battery as far as possible to see what it is capable of. Also, when choosing an inverter, make sure that it’s a Pure Sine Wave inverter to ensure that your appliances run the way they’re supposed to.
Heater Test
So for the first test, I did with this battery through the inverter powering a Lasko heater. I had an electricity monitor connected to the inverter to tell me what was happening regarding Watt Hour (Wh) pulled from the battery and the wattage output the appliance was drawing. I set the Lasko heater to low first and ended up with an 850W output; this is not a problem for the Redodo battery to handle as it’s capable of a 1280W continuous power output. After running it at low for about a minute, I set the heater to high, and the output jumped to about 1400W. With a 1400W output, the heater is over the 1280W output of this Redodo battery, but it still keeps running.
I kept running the Lasko heater for 47 minutes until the battery was completely depleted. So you can run a 1400W load from an inverter using this Redodo battery, and it can handle it for nearly an hour. Also, I got an AC capacity of 1,100Wh, which is a 86% efficiency rating when it comes to using an inverter with the battery; this type of conversion through an AC outlet is better than most power stations.
Electric Cooktop Toaster Oven Test
For the next test, I used a 1000W electric cooktop and placed a saucepan with four cups of water on top to see how fast I could boil water and how much capacity I use up. The cooktop pulled about 950W; it took about 8 minutes for the water to boil and used up 120Wh of the Redodo battery’s capacity. So you can easily cook with a high enough wattage inverter using this battery, and you won’t lose much capacity.
For the final test, I used a toaster oven to power from this battery and inverter. I set the toaster oven to 450 ° F and had to run it for about 10 minutes. The toaster oven pulled 1170W and used about 120Wh capacity from this Redodo battery. So you can easily have food toasted with this battery, too.
Overall, a 12V/100Ah battery is best to own. Going lower on the Amp Hour (Ah) scale means having lower wattage usage and less capacity to use, which ultimately means a shorter runtime. Going with a higher capacity battery means spending more, but at the same time, you get so much more capacity and wattage usage. That said, 100Ah batteries are the sweet spot for price and function.
Recharging the Battery:
You can use any 14.4V or 14.6V battery charger to recharge this Redodo 100Ah battery. In my case, I used an Ampere Time 10 Amp battery charger to recharge the unit. This is one of the lowest-cost battery chargers you can get, but it’s also one of the slowest ways to recharge. This Ampere Time 10 Amp battery charger works the same way as any other one. I just attached the negative and positive clamps to the negative and positive terminals on this Redodo battery, and it began charging.
The light on the Ampere Time battery charger turns red to indicate that it’s charging, and then it turns green to indicate that the battery is fully recharged and charging stops. Of course, as I mentioned before, a 10 Amp battery charger is relatively slow, and going from 0% to 100% will take about 10 – 12 hours.
Size and Weight:
This Redodo 100Ah battery has a length of 13 inches, a width of 6.7 inches, and a height of 8.4 inches. The battery weighs 25 pounds. So it’s not a large battery, but it has some weight. The battery does have a handle strap that makes it easier to move around, and you can also easily remove the handle if you want.
Functional Components:
In this case, when it came to using the battery with the Renogy 2000W inverter, I connected the negative and positive terminal cables from the inverter to the battery. Once the terminal ends were screwed onto the battery, I could turn on the inverter and power the appliances.
Structure and Material:
The build quality of this Redodo battery is good. The battery has an IP65 water resistance rating, meaning it can withstand rain and high-pressure jets but cannot withstand water submersion. The casing is solid, and I couldn’t find any flaws with its build quality. However, you shouldn’t drop this battery, as I’m not sure if the casing can survive a fall, as most batteries are not exactly built up to that standard.
Tech:
For the technical build, this Redodo battery has overcharge, over-discharge, temperature, short circuit, and all other protections to ensure that it performs smoothly and that you’re safe. In my heater test, when I had the heater running at about 1400W, this battery could keep supplying power to the Renogy inverter. If the battery got too hot, it would automatically shut off, but that didn’t happen in my test, as it could fully deplete its capacity.
Reliability
The testing I’ve conducted from the MakerHawk load tester and the Renogy inverter shows that this Redodo 100Ah battery is very reliable. It has the capacity it says it has a little more. Also, it uses a LiFePO4 battery cell which gives many charge cycles that allow the battery to last for many years. On the inverter side, I could power a Lasko heater at 1400W, above the 1280W that this battery is capable of. The inverter AC capacity pulled 86% efficiency from this Redodo battery.
So, this is very reliable for a 100Ah LiFePO4 battery.
Summary:
This 1280Wh capacity is precisely what you’re getting, and just a bit more because of the load test I ran. This battery can also handle loads over its 1280W max continuous output, as I ran a 1400W load for nearly an hour.
This battery is pretty small, but it does weigh 25 pounds. The removable handle does make it easier to carry the battery. Connecting the inverter was very easy, and recharging was simple, too.
The build quality of this Redodo battery is solid because of its IP65 water resistance rating. It also has many technical protections that ensure it will be safe, such as overload, short circuit, and temperature control protections.
If you want an all-around reliable battery, a 100Ah battery is the one to go with, as it has tons of capacity, power input, and output capabilities, and it comes at an affordable price compared to a 1280Wh power station.
Conclusion:
This Redodo 12V 100Ah LiFePO4 battery is an excellent choice because it’s exactly what it says it is. This 1280Wh battery can supply more than 1280W of power through an inverter; of course, you shouldn’t do that frequently with a battery like this, but I was able to run 1400W for almost an hour. Also, for a 1280Wh capacity and even adding on the cost of an inverter and a battery charger, this Redodo battery can be a better choice than an equivalent power station.
Volt, Amps, Amp-hour, Watt and Watt-hour: terminology and guide
We understand that all this terminology can be a bit confusing at times but once you know how it works it is quite simple. Below we will try to explain what it all means.
Volt or Voltage (V):
The number of volts is the amount of energy given to an electronic circuit. By a circuit we mean, for example, an electronic device. With a 12V device, 12 volts are always “given” from the battery. A battery always has a fixed voltage (e.g. 12, 24, or 36 volts) and a device always works at a certain voltage. For example, a device that works on 12 volts obviously needs a battery that also supplies 12V.
Current – Ampere (A):
When we talk about amperes (or amps), we are talking about how much electricity “flows” per second. If the number of amps goes up, then current flowing through the device per second also goes up. An electrical device usually works on a fixed voltage, but the amount of amps it draws can vary depending on, for example, the position of your trolling engine (a trolling engine at full throttle draws more amps than in half throttle for instance).
Example 1: Suppose I have a Minn Kota Endura C2 50 LBS that I am running on gear / speed setting 2. The trolling engine runs on 12V and currently draws 15A. I decide to go a little faster and I switch to gear / speed setting 4. The engine still runs on 12V but now pulls 25A. The voltage has remained the same but the number of amps has gone up.
Power – Watts (W): :
Power is the voltage multiplied by the number of amps, or W = V x A. This is the amount of energy consumed by a device and therefore an indication of how powerful it is. This goes up when the number of amps also goes up.
Example 2: Suppose I have a 24V Minn Kota Terrova 80 LBS bow motor that draws 30 amps. So the power consumption is 24 x 30 = 720W.
Example 3: Suppose I have another Minn Kota Endura C2 50 LBS that I am running in gear / speed setting 2. The engine runs on 12V and draws 15A and thus has a power consumption of 180W (12 x 15). When I switch to gear / speed setting 4, the engine draws 25A and still runs on 12V. The power consumption of the trolling motor is now 300W.
Capacity – Amp hours (Ah):
Battery capacity is measured in Ah, or Amp-hours. As the name suggests this means how many amps the battery can deliver in an hour. For example, a 12V lithium battery with a capacity of 100Ah can deliver 100A to a 12-volt device for one hour. The same 100Ah battery could supply power for 4 hours (100/25=4) to a 25 ampere device. If a battery has 12V50, this means that the battery works on 12 Volt and has a capacity of 50Ah. A 24V100 battery works on 24 Volt with a capacity of 100 Ah etc. In practice for lead-acid batteries the nominal capacity (how many Amps hours the battery can deliver according to specifications) differs greatly from the effective capacity (how many Amps the battery can actually deliver during use). We explain how this works in our article discharge and battery capacity.
Example 4: I run my Minn Kota Endura C2 50 LBS in gear / speed setting 2, drawing 15A at 12V. I have a 12 volt battery of 70 ah. My total run time is now 70 / 15 = 4.7 hours. When I switch to gear / speed setting 4 the engine draws 25A. My total runtime is now 70 / 25 = 2.8 hours.
Capacity – Watt-hour (Wh):
Another way to measure the capacity of the battery is in Watt-hours (Wh). Wh is calculated by multiplying the number of Amps with the battery voltage. For example, a 12V100 (a 12 volt battery with a capacity of 100Ah) has a capacity of 12 x 100 = 1200Wh. A 24V50Ah battery has a capacity of 24 x 50 = 1200Wh. So these batteries have the same capacity, only one works on 12 volts and the other on 24 volts. In practice you will notice that these batteries will be around the same dimensions and weight.
Example 5: I have a 600W trolling motor and a battery with a capacity of 1200Wh. My runtime at full throttle is 2 hours with this battery (1200 / 600 = 2). I do not even need to know how the trolling engine or battery voltage to calculate this (as long as they work at the same voltage obviously).
The attentive reader notes that the runtime of a battery with a device can be calculated in two ways. Either by dividing the number of Amps of the battery by the power draw in A of the trolling motor or by dividing the number of Wh of the battery Wh by the number of W of the trolling engine.
Connecting batteries: in series and parallel
Batteries can be connected together to achieve a higher voltage or higher capacity. This is done by connecting the battery terminals of the batteries with cables.
Connecting in series: higher voltage, equal number of Ah
When we say that we connect batteries in series, we connect the plus terminal of one battery to the minus terminal of another battery. This means that you still have a minus terminal available on one battery and a plus terminal available on the other battery. The electrical device should be connected to these two available battery terminals. If we connect batteries in series, the voltage goes up, and the capacity measured in Ah remains the same.
In the picture above we see two 12V50Ah batteries. As you can see the two batteries are connected in series: the minus and plus terminals are connected together. You have created a 24V50 battery : 24V (due to series connection) with 50Ah capacity (number of Amps remains the same). If we measure the capacity in Watt-hours, the total capacity is now 24 x 50 = 1200 Wh.
Connecting in Parallel: equal voltage, higher number of Amps
When connecting batteries in parallel, we connect the minus terminal of one battery to the minus terminal of the other battery and the plus terminal of one battery to the plus terminal of the other battery. We connect the minus wire of the electrical appliance to one of the minus terminals and the plus wire to the plus terminal of the other battery (see the picture below). The same voltage is now supplied but the number of Amps has increased.
In the picture above, the minus terminals of both batteries are connected and the plus terminals are connected. So the battery is connected in parallel. There is still 12 Volt but the number of Amps has increased from 50 to 100. We have now created a 12V100Ah battery. If we measure the capacity in Watt-hours, the total capacity is now 12 x 100 = 1200 Wh.
So the number of watt-hours always remains the same, whether you connect them in series or parallel.
Attention: always check whether batteries are suitable to connect together. Only connect identical batteries (same type/model, age and charge status) and use cables of the correct thickness and length. We recommend that you do not connect 12 volt Rebelcell batteries in series but instead select a Rebelcell 24 volt battery. Rebelcell 24 volt batteries can be connected in series up to 48V without any problems.
Other terminology relating to batteries
The technical specification for batteries often includes many other terms. Below we will try explain what the most important ones mean.
Voltage: this is the voltage that the battery delivers on average. As explained above, the battery starts with a higher voltage than when it is partially discharged. With this we mean the average of this progression or the nominal voltage.
Chemistry: this indicates what kind of lithium battery technology is used.
C1, C5, C20: this indicates battery capacity when discharged in a certain number of hours. C20= 100Ah means that the battery can deliver 100 ampere hours if it is discharged in 20 hours (with 5A). Lead batteries have a lower capacity if they are discharged faster. For example, a lead-acid battery can deliver 100Ah if it is discharged in 20 hours (C20=100), but if the same battery is discharged in 5 hours it will only deliver 70Ah (C5=70). With Rebelcell batteries it doesn’t matter if you discharge them in 20 hours, 5 hours or 1 hour, they always deliver the same capacity. That is why we always refer to our capacity as Capacity (C1-C20). Read more about this in our article about effective battery capacity.
EqPb: this stands for ‘equivalent lead battery’. By this we mean that this battery can be compared to a lead battery with the indicated capacity when used in combination with an electric motor. Often a lithium battery with a much lower Ah can in practice deliver the same amount as a lead-acid battery with a much higher Ah. In practice, for example, the Rebelcell 12V50 can be compared to a 105Ah semi-traction battery in terms of operating time for an electric motor. This also has everything to do with the usable battery capacity.
Nominal energy: this is the battery capacity measured in watt-hours (see above for explanation).
Maximum continuous discharge: this is the maximum number of amps the battery can continuously deliver. Suppose a battery has a maximum continuous discharge of 30A, then you cannot connect a device that draws more than 30A. The higher the capacity of the battery, the higher the maximum continuous discharge.
Peak discharge (10 milli-sec): this is the maximum number of amps the battery can deliver for 10 milli-seconds. This is always higher than the maximum continuous discharge. Some equipment has a short peak discharge when starting up (so called ‘inrush’ currents). This is for example the case when you go from zero to full throttle in one go with an electric outboard engine. At that moment, the motor requires more amps than the rated maximum for a short time.
Lifespan (#charges) (@80%DoD): this indicates how often you can discharge and recharge the battery up to a certain percentage. For example, if it says “Lifetime (#charges) (@80%DoD): 1500” it means that the battery can be discharged to 80% for 1500 times (i.e. with 20% capacity left). For example, if it says “Lifetime (#charges) (@100%DoD): 1000” then the battery can be fully discharged 1000 times.
Energy density: with this we measure the number of Watt-hours per kilo of battery. Energy density is much higher for lithium batteries than for lead-acid batteries. A high energy density means that you can store more energy in the same space. And this results in a lighter and smaller battery.
Bandwidth voltage: see explanation of the discharge and capacity of batteries. This gives the minimum voltage (at 0%) and the maximum voltage (at 100%) of the battery.
Charge temperature: this gives the minimum and maximum temperature at which a battery can be charged.
Discharge temperature: this indicates the minimum and maximum temperature at which a battery can be discharged.
Storage temperature: This indicates the minimum and maximum temperature at which a battery can be stored safely.
Maximum charge current: This gives the maximum current in A at which the battery can be charged. The higher this number, the faster the battery can be charged (with the right battery charger).
Integrated cell balancing: part of the Battery Management System. The cell balancing feature ensures that the voltage of individual lithium battery cells is equalised, so the cells all have the same charge status / voltage. This is necessary for optimal use and performance of the battery.
Temperature protection: part of the Battery Management System. The battery is switched off when the temperature becomes too high or too low. This is a protection to prevent damage.
Maximum discharge current protection: part of the Battery Management System. The battery is switched off when the power draw of your equipment is higher than is allowed. This is a protection to prevent damage.
Overvoltage protection: part of the Battery Management System. The battery is switched off when the voltage becomes too high and the battery is overcharged. This is a protection to prevent damage.