Battery Management 101. Battery boost voltage


The battery gives your vehicle its get-up-and-go and a whole lot more. Without it, you couldn’t raise and lower the Windows, lock the doors or keep the music playing. So, when something plays such a big role in your life behind the wheel, it’s just natural to wonder how it works.

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When discussing car battery voltage, we’re generally talking about a 12-volt battery. When we take a closer look, we see car battery voltage can range anywhere from 12.6 to 14.4.

  • With the engine off, the fully charged car battery voltage will measure 12.6 volts. This is known as “resting voltage.”
  • When the engine is running, battery voltage will typically rise to 13.5 to 14.5 volts. The battery is boosted to these higher levels by the alternator.

To better explain, let’s take a step back and look at the integral role the typical 12-volt battery plays in your vehicle’s starting and charging system.

  • The battery stores electrical energy.
  • The starter converts the electrical energy to mechanical energy to crank the engine.
  • After the engine has started, the alternator produces an electric current that replaces the energy the starter drew from the battery.

These three steps repeat, over and over, powering your engine as the electrical energy is again converted to mechanical energy and the alternator recharges the battery to supply additional current.

Now that we’ve looked at how many volts in a car battery and how the battery works, we’re ready to move on to amperage.

Amperage, or amps, is a way to describe car battery current. The amperage rating is going to differ based on the number of options your vehicle has. Simply put: a highly-optioned vehicle is going to have a higher amperage battery. The typical battery amperage ranges from 450 to 750 CCA.

Hey, wait a minute! What’s CCA? CCA stands for cold cranking amps, and refers to the number of amps a 12-volt battery can deliver at 0ºF for 30 seconds while maintaining a voltage of 7.2 volts or more. The higher the CCA, the greater the starting power.

Proper maintenance can help your battery keep working as designed. Typically, it’s recommended that the battery be inspected at least every 6 months/6,000 miles. The schedule for your specific vehicle outlined in your owner’s manual. No manual? No problem! Jiffy Lube ® technicians can access your vehicle’s maintenance schedule and the recommended procedures.

If you experience battery problems but you’re between scheduled maintenance checks, please don’t hesitate to have your vehicle checked. Symptoms of battery trouble include:

  • Dim lights (headlights and/or interior lights)
  • “Check Engine” or “Charging” lights are illuminated
  • Accessories like power seats and Windows fail to operate


Your battery is complex and key to your engine’s performance. That’s why you should bring your vehicle to Jiffy Lube for battery care. When you bring your vehicle to one of the 2,000 locations around the country for a battery check, expect a trained Jiffy Lube technician to:

  • Ask questions about your driving style to determine the impact it may have on your vehicle’s starting and charging system
  • Visually inspect your battery, including the hold down and connections
  • Perform a thorough terminal cleaning (as needed with your approval)
  • Replace cables (as needed with your approval)
  • Inspect connections and tighten them, if required
  • Use a multimeter to test your battery strength
  • Inspect and adjust your battery fluid level (if possible)

Remember, consistent and careful battery maintenance can help prolong battery life and keep your starting/charging system running efficiently.


Preventive maintenance, performed by highly-trained technicians, can help save you two of your most valuable resources:

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  • Time. Commuting to work, carpooling to school, grocery shopping … you need your car! Preventive maintenance can help you avoid a major repair that could keep your vehicle off the road and in the shop for days (or even weeks).
  • Money. Catching a small problem when it’s still a simple fix can save you the cost of an expensive repair.


If you have ever wondered how long a car battery usually lasts, find out here.

Please return to Tips in a Jiffy often, because new content is added regularly.

Please note: Not all services are offered at all Jiffy Lube service centers. Please call ahead or check to ensure the service is available.

Battery Management 101

Many RV owners may not have the technical background to understand the operation of their battery charger. Sometimes they forget about the need to maintain the battery water level and to keep it fully charged when their RV is in storage.RV owners do however remember the consequences of improper battery charging and maintenance…a dead battery that is expensive to replace!

The following analogy uses the flow of water from a Charger Tank (battery charger) to fill (recharge) a Battery Tank (battery) to simulate a battery recharging cycle. The goal is to fill (recharge) the Battery Tank as fast as possible, while keeping water loss to a minimum. The same goal you have when recharging your RV battery. This analogy explains the need to constantly monitor and adjust the flow rate to prevent water loss. Battery chargers also require voltage adjustments during the recharge cycle to reduce water loss. The small leak at the bottom of Battery Tank represents the small internal current leak present in all lead acid batteries. This internal current leak self-discharges your RV battery approximately 4% per week, thus the need to charge your battery periodically when in storage.

At the start, both tanks shown below are at the same height, 12.6 feet; therefore, water (amps) in the Charger Tank will not flow into Battery Tank. Water will only flow if the height of Charger Tank is increased. Remember when recharging your RV batteries the charger voltage must also be higher than battery voltage to allow charging current to flow.Typical converters/chargers used in the RV Industry have a fixed output voltage of 13.6 volts.

As Battery Tank begins to approach the 90% Full Level the Charger Tank must be lowered to 13.6-Ft. (figure # 4) to prevent excess splashing and water loss over the top. The Battery Tank would then complete the fill at this slower rate.

In figure the Battery Tank is now full, but the Charger Tank continues to remain at 13.6-Ft. This causes more water to flow than required to maintain a full level in the tank. This excess water is lost as it splashes out the top of the Battery Tank.

To reduce water loss even more, once the Battery Tank is fully charged the height of Charger Tank must lowered to 13.2-Ft. This lower height reduces the flow from the Charger Tank so that it just equals water lost due to the leak at the bottom of Battery Tank.

As you have seen filling a Battery Tank as fast as possible with minimum loss of water, requires several adjustments to the height of the Charger Tank. First, it has to be raised to 14.4 feet to refill as fast as possible. Then it must be lowered to 13.6 feet to finish the fill with minimum water loss. Once the tank is full, you have to lower it again to 13.2 feet to reduce water loss even further.

Proper recharging of RV and Marine batteries also requires charger voltage adjustments during charging cycle to accomplish these same benefits. Unfortunately, most battery converter/chargers on the market today have a fixed output voltage of 13.6 volts and can not be adjusted.

It would be nice if someone created a robot called the “Battery Butler” that automatically came around every week to check and adjust your battery system. Well someone has, Progressive Dynamics developed a microprocessor based programmer-controller for our electronic power converters. This device proved to be so intelligent, we called it the Charge Wizard, because it automatically adjusts the charging voltage as required by the battery to ensure fast recharge cycles, with minimum water loss.

Now that you understand the requirements for properly filling a tank with water, it is time to learn more about the construction operation and recharge requirements of your RV and Marine lead acid batteries.

Since a single lead-acid cell only produces 2.1; volts, six (6) cells must be connected in series to create the typical RV or marine battery (see Figure below). Six cells connected in series will provide a total voltage output of 12.6-volts. The standard RV battery (shown below) has an output voltage of 12.6 volts, when fully charged!

The Battery Discharge Cycle

In figure below, the battery is partially discharged and Lead Sulfate (sulfation) has begun to coat both lead plates. The output voltage of the battery has dropped to 12.3 volts.

In figure below, the battery has now been discharged to 50% of its total capacity. The Lead Sulfate (sulfation) is now covering more of the surface area of the plates. The battery voltage has dropped to 12.1 volts.

Figure #11 below illustrates a fully discharged battery and the voltage has dropped to 10.5 volts. Battery Management 101 now completely covers the surface of all plates. Initially the Lead Sulfate coating is soft, thin and easily reconverted into lead and sulfuric acid when battery is recharged. It is important to remember, The longer your battery remains discharged, the more it will begin to form hard crystals of Lead Sulfate…RECHARGE YOUR BATTERY AS SOON AS POSSIBLE! Once these hard crystals form, they are impossible to remove during a standard fixed voltage (13.6 volts) charging process.

Now that the battery is completely discharged it is time to discuss the recharge cycle. Remember, when recharging your RV battery the goal is to recharge it as fast as possible without excess water loss.

Recharging Lead Acid Batteries with the Charge Wizard

In figure below, the battery is in the process of being recharged. The Charge Wizard has detected the battery is very low and has automatically selected BOOST MODE (14.4 volts), of operation to return battery to 90% of full charge in 2-3 hours.

In figure # 13, the battery has reached the 90% of full charge level. The Charge Wizard has reduced charging voltage to 13.6 volts to prevent excess battery gassing and water loss. The remaining 10% of charge cycle will be completed at this lower voltage.

When the battery reaches full charge (figure # 14), charging voltage must be reduced to 13.2 volts. This lower voltage reduces charging current to 20 to 25 milliamps, enough to replace current lost through the internal leakage present in all batteries. The Charge Wizard knows this and automatically selects STORAGE MODE of operation and reduces charger voltage to 13.2 volts.


When electrical current flows through water during the charging cycle, it breaks the water down into its original components, a mixture of Hydrogen Oxygen. These two gasses are extremely flammable and can cause an explosion if the battery is not properly vented to the outside of the RV. This normal conversion of water into hydrogen and oxygen is part of the battery recharge cycle and is another reason you should check the battery water level at least once a month.

Other Battery Maintenance Problems Solved by the Charge Wizard

Even after receiving a full charge, notice that near the bottom of the battery, some of the Lead Sulfate has not converted back into lead and sulfuric acid. This remaining Lead Sulfate has formed hard crystals that can not be easily reconverted. These hard crystals are the beginning of BATTERY SULFATION, the leading cause of battery failure.

To remove the remaining Lead Sulfate, the battery must receive an EQUALIZING CHARGE (i.e. increase the charging voltage to 14.4 volts or higher periodically for a short time). This equalizing charge will eventually convert this crystallized Lead Sulfate into its components (lead and sulfuric acid).

Problem solved the Charge Wizard automatically provides an EQUALIZING CHARGE that increases charging voltage from 13.2 to 14.4 volts for 15 minutes every 21 hours, when operating in the STORAGE MODE. The Charge Wizard’s EQUALIZATION MODE automatically eliminates BATTERY SULFATION BUILD-UP before it becomes a problem! Remember that the rate of SULFATION increases rapidly as a battery discharges…so keep your battery fully charged when not in use!

Now that you have seen what the Charge Wizard can do to improve battery recharge time, adjust charge voltages to reduce water loss, and eliminate sulfation, its time to eliminate the last of the battery plagues…BATTERY STRATIFICATION!

What is BATTERY STRATIFICATION? You learned previously that the electrolyte inside a battery is a mixture of water and sulfuric acid and like all mixtures, one component is heavier than the other is. In this case Sulfuric Acid is the heavy component and will eventually begin to settle to the bottom of the battery. This process is called STRATIFICATION!Stratification will increase build-up of lead sulfate and reduce battery capacity.

The way to prevent BATTERY STRATIFICATION is to apply an EQUALIZING CHARGE (i.e. increase charging voltage to 14.4 volts) to your fully charged battery for a short period at least once a month. This EQUALIZING CHARGE will cause heavy gassing. This heavy gassing mixes up the electrolyte and equalizes the water/sulfuric acid mix. Equalizing also breaks down lead sulfate crystals that may have begun to form. The Charge Wizard automatically Equalizes your battery for 15 minutes every 21 hours, when in the STORAGE MODE to prevent BATTERY STRATIFICATION.

As you have learned, the Charge Wizard is a very valuable addition to your battery charging system and it will eliminate battery problems. Charge Wizards are available at leading RV Dealers and Distributors, or you may contact Progressive Dynamics at 269 781 4241. ORDER YOUR CHARGE WIZARD TODAY AND ELIMINATE BATTERY PROBLEMS.

Answers to Common Questions about Batteries

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Perform this test when installing.

Lead Acid Battery Voltage Charts (6V, 12V 24V)

Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.

Here are lead acid battery voltage charts showing state of charge based on voltage for 6V, 12V and 24V batteries — as well as 2V lead acid cells.

Lead acid battery voltage curves vary greatly based on variables like temperature, discharge rate and battery type (e.g. sealed, flooded). The voltage to battery capacity chart in your battery manual should always take precedence over the generic, averaged ones listed below.

Note: Estimating state of charge based on open circuit voltage is only accurate when batteries are at room temperature and have been resting — i.e. disconnected from all loads and chargers — for several hours.

V Lead Acid Battery Voltage Charts

Printable Chart


6V lead acid batteries are used in some DC devices like lights, pumps and electric bikes. You can also wire two in series to create a 12V battery bank. They are made by connecting three 2V lead acid cells in series.

6V sealed lead acid batteries are fully charged at around 6.44 volts and fully discharged at around 6.11 volts (assuming 50% max depth of discharge).

6V flooded lead acid batteries are fully charged at around 6.32 volts and fully discharged at around 6.03 volts (assuming 50% max depth of discharge).

V Lead Acid Battery Voltage Charts

Printable Chart


12V lead acid batteries are popular in solar power systems and other 12V electrical systems. They’re widely available and have a low upfront cost. Many car and marine batteries are 12V lead acid batteries. They are made by connecting six 2V lead acid cells in series.

As far as I can tell, lead acid is still the most popular rechargeable battery type for DIY solar power systems. Lithium iron phosphate (LiFePO4) batteries have become a lot more popular in recent years, though, in large part thanks to their dramatic price drops we’ve seen over the last decade.

12V sealed lead acid batteries are fully charged at around 12.89 volts and fully discharged at around 12.23 volts (assuming 50% max depth of discharge).

12V flooded lead acid batteries are fully charged at around 12.64 volts and fully discharged at around 12.07 volts (assuming 50% max depth of discharge).

V Lead Acid Battery Voltage Charts

Printable Chart


24V lead acid batteries are another common option for solar power systems. Working with higher voltages helps keep amperage low, saving you money on wiring and equipment. They are made by wiring in series twelve 2V lead acid cells or two 12V lead acid batteries.

24V sealed lead acid batteries are fully charged at around 25.77 volts and fully discharged at around 24.45 volts (assuming 50% max depth of discharge).

24V flooded lead acid batteries are fully charged at around 25.29 volts and fully discharged at around 24.14 volts (assuming 50% max depth of discharge).

V Lead Acid Cell Voltage Charts

Printable Chart


Individual lead acid cells have a nominal voltage of 2 volts (sometimes listed as 2.1 volts). You can buy 2V lead acid cells and connect them in series-parallel configurations to build a battery bank with your desired voltage and capacity.

2V sealed lead acid cells are fully charged at around 2.15 volts and fully discharged at around 2.04 volts (assuming 50% max depth of discharge).

2V flooded lead acid cells are fully charged at around 2.11 volts and fully discharged at around 2.01 volts (assuming 50% max depth of discharge).

Ways to Check Lead Acid Battery Capacity

Measure Open Circuit Voltage with a Multimeter

Pros: Accurate

Cons: Must disconnect all loads and chargers and let battery rest for several hours

To properly estimate battery capacity based on open circuit voltage, first disconnect everything from your battery and let it rest at room temperature for several hours. (Battery University recommends at least 4 hours.)

Then, simply use a multimeter to measure the voltage at the battery terminals and compare the number you get to the state of charge chart in your battery manual. If your battery manual doesn’t have a chart, use the relevant one listed above.

For example, I recently wanted to test the remaining capacity of a 12V 33Ah sealed lead acid battery I own. The battery was already at rest and at room temperature — it had been sitting disconnected in my basement for the past couple weeks.

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So I grabbed my multimeter, prepped it to measure DC voltage, and touched the probes to the battery terminals. I got an open circuit voltage of 12.63 volts.

I couldn’t find my battery’s manual, so I referred to the 12V sealed lead acid voltage chart above to estimate its capacity. Based on that chart, I’d estimate it had about 80% capacity left.

Check Specific Gravity with a Hydrometer or Refractometer

Pros: Accurate

Cons: Only works for flooded lead acid batteries

You can use a hydrometer or refractometer to measure what’s called the specific gravity of your lead acid battery. Measuring the specific gravity is another way to estimate state of charge.

Because this method requires you to open the battery to access the electrolyte solution inside, it only works with flooded batteries.

I’ve only ever used sealed lead acid batteries, so I unfortunately can’t run you through the steps on how to do this. Refer to the steps listed in your battery manual, or the product manual for your hydrometer or refractometer.

Use a Solar Charge Controller

Pros: Convenient

Cons: Inaccurate

If you’re using your lead acid battery in a solar power system, your charge controller probably measures battery voltage for you.

You may be thinking you can just use this reading to get an accurate estimate of your battery capacity. Unfortunately, using battery voltage to estimate capacity while the battery is connected to chargers and loads is very inaccurate.

Battery voltage varies greatly depending on factors like temperature and rate of discharge. Plus, the battery voltage reading given by some charge controllers can be inexact. Some charge controllers only display one decimal place, and others have wide margins of error. For example, one cheap PWM charge controller I tested claimed a battery voltage margin of error of ± 0.2 volts.

Still, I know most DIY solar enthusiasts will use this reading most often, if not exclusively. It’s a hassle to disconnect everything from your battery and let it rest just to measure its state of charge more accurately.

If that’s you, just keep in mind how inaccurate this number can be. Don’t think you can know the precise state of charge of your battery from it. Just use it to get a general idea of whether or not your battery is close to being fully charged or discharged.

Lead Acid Voltage FAQ

Note: To reiterate, the recommended voltages and state of charge chart in your battery’s manual should take precedence over the generic ones listed below.

What is the voltage of a fully charged 12V lead acid battery?

A 12V sealed lead acid battery will have an open circuit voltage of around 12.9 volts when fully charged.

A 12V flooded lead acid battery will have an open circuit voltage of around 12.6 volts when fully charged.

To accurately estimate a battery’s capacity based on its voltage, you must first disconnect all loads and chargers from the battery and let it rest at room temperature for several hours.

What is the minimum voltage of a 12V lead acid battery?

The minimum open circuit voltage of a 12V sealed lead acid battery is around 12.2 volts, assuming 50% max depth of discharge.

The minimum open circuit voltage of a 12V flooded lead acid battery is around 12.1 volts, assuming 50% max depth of discharge.

How much can you discharge a lead acid battery?

Many lead acid batteries can only be discharged up to 50%. Discharging them more can cause permanent damage. You should never completely discharge a lead acid battery to 100% depth of discharge. Doing so can shorten its lifespan greatly.

Here is a graph showing the relationship between depth of discharge and life cycles for non-deep-cycle lead acid batteries:

As you can see, consistently discharging a lead acid battery to 100% can severely shorten its lifespan.

What is the float voltage of a 12V lead acid battery?

The float voltage of a sealed 12V lead acid battery is usually 13.6 volts ± 0.2 volts.

The float voltage of a flooded 12V lead acid battery is usually 13.5 volts.

battery, management, boost, voltage

As always, defer to the recommended float voltage listed in your battery’s manual. Some brands refer to float as “standby.” Sometimes, the float voltage will even be listed on your battery label.

How I Got the Numbers in These Charts

To get the numbers in the voltage tables above, I looked up the datasheets for 7 popular brands of lead acid batteries. I found the state of charge charts in each and averaged them together for the final values.

Here are the datasheets I used for the sealed lead acid values (2 AGM, 2 gel), along with the page number where I found the voltage chart:

And here are the ones I used for the flooded values:

Creating these charts was far from an exact science. Only a couple of the datasheets listed open circuit voltages by capacity in table format with exact numbers. Often, they included a graph from which I’d have to infer the numbers. What’s more, the graphs often had wide bands rather than thin lines, as if to convey a margin of error or range of possible values — what I came to see as the brands hedging against providing an exact number.

Other brands provided exact numbers, but only for 0%, 25%, 50%, 75%, and 100% capacity values. From these I had to create linear functions to estimate the values between them.

I calculated all the numbers for 2V lead acid cells first, then multiplied these values by the respective number of cells in series to get the values for 6V, 12V and 24V batteries. Finally, I rounded all the values to two decimal places.

Using a car battery charger

Frequent short trips, with constant stopping and starting, make your battery work very hard, especially in winter when heater, headlights. heated Windows and wipers may be working most of the time.

Eventually, because more current is being drained from the battery than the alternator can put back, the battery will not have enough power left to turn the starter motor. A battery in that state of discharge is said to be flat.

A flat battery can be avoided if you have a battery charger. a relatively cheap, but worthwhile accessory.

It uses mains current to replace the battery’s lost charge through positive and negative leads that clip to the corresponding battery posts.

An average car battery has a capacity of around 48 amp hours which means that, fully charged, it delivers 1 amp for 48 hours, 2 amps for 24 hours, 8 amps for 6 hours and so on.

A basic charger usually charges at around 2 amps. and so needs 24 hours to deliver the 48 amps needed to fully charge a flat, 48 amp hour battery.

But there is a wide range of chargers with different charge rates on the market. from 2 to 10 amps. The higher the charge output, the faster a flat battery is recharged. Fast charging, however, is undesirable as it can buckle the battery plates.

The loads imposed on your battery may be gauged from the amount of current used by the various electrical components: headlights take about 8 to 10 amps, a heated rear window about the same.

Theoretically, a fully charged battery, without taking in current from the generator. should work the starter for about ten minutes, or the headlights for eight hours, and a heated rear window for 12 hours. As the battery nears full discharge, the lights gradually grow dimmer and finally go out altogether.

There are also causes other than short trips and cold weather which can affect the state of your battery. Failure is more common on cars equipped with a dynamo rather than an alternator. because the alternator produces more electricity and charges better at low engine speeds (See How the charging system works ).

The answer in all these cases is frequent testing with a hydrometer (See Checking the batteries ) to see how much capacity is left in the battery, and using a battery charger to top up its charge when necessary.

Connecting a battery charger

Always check the electrolyte level before connecting the battery to the charger. Top up if necessary (See Checking the batteries ) and clean the battery posts.

If there is a power point handy, the battery can be left in the car, so long as the charge rate is only 3 or 4 amps.

However, if the car has an alternator, disconnect the battery terminals beforehand: otherwise some alternators. generally the older type. can be damaged.

If separate cell caps are fitted, remove them for ventilation. Leave a trough cover on, unless the charging rate is high. Clamp the positive lead from the charger, usually coloured red, to the positive battery post. Clamp the negative (-) lead, usually black, to the negative terminal.

Plug the charger into the mains and switch on. The indicator light or gauge ( ammeter ) will show that the battery is being charged.

The gauge may show a high charging rate at first, but this drops gradually as the battery becomes charged.

If it was very flat, charging is likely to take a long time; check periodically with a hydrometer, while continuing the charge.

In the final stages, the cells bubble and give off gas. If any of them begin gassing before others, or do so more violently, the battery is probably defective and should be checked by a garage or battery specialist.

Types of car battery charger

A basic home battery charger incorporates a transformer and rectifier, to change the mains 110/220 volt alternating current to 12 volt direct current. and allows the mains supply to provide a charging current at a rate determined by the state of the battery.

In the case of a battery in good condition, the rate of charge may be around 3 to 6 amps with a normal home charger.

A battery at the end of its useful life may not accept any recharging, and will not, in any case, hold a charge.

Some chargers are fitted with a high and low (Hi-Lo) switch to give a choice of two charging rates. typically 3 or 6 amps. in case you want to give the battery a short overnight boost at 6 amps rather than a longer charge at 3 amps.

Many have a charge indicator which may be a warning light, or a gauge showing the charge rate in amps.

Read more

How to test a car battery

If your car’s instrument panel includes an ammeter. it will tell you how well the charging syst.

Checking the batteries

Most car batteries are sealed for life. apart from a small vent hole which allows gas to e.

Checking a starter circuit

If the starter does not turn the engine although the car battery is in good condition, the.

How to test electrical circuits

If there is trouble without an obvious cause in any electrical component, test the circuit to f.

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