Deep Cycle Battery FAQ
The links below are on this page. you can also just scroll down if you want to read them all.
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- What is a Battery?
- Types of Batteries
- Battery Lifespan
- Starting, Marine, or Deep Cycle?
- Deep Cycle Battery as a Starting Battery?
- What Batteries are made of
- Industrial Deep Cycle Batteries (forklift type)
- Sealed Batteries
- Battery Size Codes
- Gel Cells (Gelled Electrolyte) (and why we don’t like them)
- AGM Batteries (and why we do like them)
- Temperature Effects
- Cycles vs Lifespan
- Amp-Hours. what are they?
- Battery Voltages
- Battery Charging (Here is where we get into the real meat)
- Charge Controllers (for wind/solar)
- Mini Factoids. Some small facts about batteries
The subject of batteries could take up many pages. All we have room for here is a basic overview of batteries commonly used in photovoltaic power systems. These are nearly all various variations of Lead-Acid batteries. For a very brief discussion on the advantages and disadvantages of these and other types of batteries, such as NiCad, NiFe (Nickel-Iron), etc. go to our Batteries for Deep Cycle Applications page. These are sometimes referred to as deep discharge or deep cell batteries. The correct term is deep cycle.
A printable version of this page will be available in Adobe PDF format when we finish updating this page for downloading and printing: Most of the charts have small images for faster downloading. To see the full size picture, just click on the small one.
What is a Battery?
A battery is an electrical storage device. Batteries do not make electricity, they store it, just as a water tank stores water for future use. As chemicals in the battery change, electrical energy is stored or released. In rechargeable batteries, this process can be repeated many times. Batteries are not 100% efficient. some energy is lost as heat and chemical reactions when charging and discharging. If you use 1000 watts from a battery, it might take 1050 or 1250 watts or more to fully recharge it.
Internal Resistance
Part. or most. of the loss in charging and discharging batteries is due to internal resistance. This is converted to heat, which is why batteries get warm when being charged up. The lower the internal resistance, the better. There is a good explanation and demonstration of Internal Resistance here.
Slower charging and discharging rates are more efficient. A battery rated at 180 amp-hours over 6 hours might be rated at 220 AH at the 20-hour rate, and 260 AH at the 48-hour rate. Much of this loss of efficiency is due to higher internal resistance at higher amperage rates. internal resistance is not a constant. kind of like the more you push, the more it pushes back.
Typical efficiency in a lead-acid battery is 85-95%, in alkaline and NiCad battery it is about 65%. True deep cycle AGM’s (such as Concorde) can approach 98% under optimum conditions, but those conditions are seldom found so you should figure as a general rule about a 10% to 20% total power loss when sizing batteries and battery banks.
Practically all batteries used in PV and all but the smallest backup systems are Lead-Acid type batteries. Even after over a century of use, they still offer the best price to power ratio. A few systems use NiCad, but we do not recommend them except in cases where extremely cold temperatures (-50 F or less) are common. They are expensive to buy and very expensive to dispose of due to the hazardous nature of Cadmium.
We have had almost no direct experience with the NiFe (alkaline) batteries, but from what we have learned from others we do not not recommend them. One major disadvantage is that there is a large voltage difference between the fully charged and discharged state. Another problem is that they are very inefficient. you lose anywhere from 30 to 40% in heat just by charging and discharging them. Many inverters and charge controls have a hard time with them. It appears that the only current source for new cells seems to be from Hungary. In the past they were often used by railroads as backup power, but nearly all have now changed over to newer types.
An important fact is that ALL of the batteries commonly used in deep cycle applications are Lead-Acid. This includes the standard flooded batteries, gelled, and sealed AGM. They all use the same chemistry, although the actual construction of the plates, etc varies.
Types of Batteries
Batteries are divided in two ways, by application (what they are used for) and construction (how they are built). The major applications are automotive, marine, and deep-cycle. Deep-cycle includes solar electric (PV), backup power, traction, and RV and boat house batteries. The major construction types are flooded (wet), gelled, and sealed AGM (Absorbed Glass Mat). AGM batteries are also sometimes called starved electrolyte or drybecause the fiberglass mat is only 95% saturated with Sulfuric acid and there is no excess liquid.
Flooded may be standard, with removable caps, or the so-called maintenance free (that means they are designed to die one week after the warranty runs out). All AGM gelled are sealed and are valve regulated, which means that a tiny valve keeps a slight positive pressure. Nearly all sealed batteries are valve regulated (commonly referred to as VRLA. Valve Regulated Lead-Acid). Most valve regulated are under some pressure. 1 to 4 psi at sea level.
Battery Lifespan
The lifespan of a deep cycle battery will vary considerably with how it is used, how it is maintained and charged, temperature, and other factors. It can vary to extremes. we have seen L-16’s killed in less than a year by severe overcharging and water loss, and we have a large set of surplus telephone batteries that see only occasional (10-15 times per year) heavy service that was just replaced after 35 years. We have seen gelled cells destroyed in one day when overcharged with a large automotive charger. We have seen golf cart batteries destroyed without ever being used in less than a year because they were left sitting in a hot garage or warehouse without being charged. Even the so-called dry charged (where you add acid when you need them) have a shelf life of 18 months at most. (They are not totally dry. they are actually filled with acid, the plates formed and charged, then the acid is dumped out).
These are some typical (minimum-maximum) expectations for batteries if used in deep cycle service. There are so many variables, such as depth of discharge, maintenance, temperature, how often and how deep cycled, etc. that it is almost impossible to give a fixed number.
- Starting: 3-12 months
- Marine: 1-6 years
- Golf cart: 2-7 years
- AGM deep cycle: 4-8 years
- Gelled deep cycle: 2-5 years
- Deep cycle (L-16 type etc): 4-8 years
- Rolls-Surrette premium deep cycle: 7-15 years
- Industrial deep cycle (Crown and Rolls 4KS series): 10-20 years.
- Telephone (float): 2-20 years. These are usually special purpose float service, but often appear on the surplus market as deep cycle. They can vary considerably, depending on age, usage, care, and type.
- NiFe (alkaline): 5-35 years
- NiCad: 1-20 years
Deep Cycle Marine Batteries
Manufactured entirely by hand, from start to finish and built to Military Specifications. As a family owned and operated US manufacturing facility, we take pride in all of our products. Our quality materials and craftsmanship put us on top in the AGM battery market. Lifeline® is a powerful name in the battery industry with world class performance and customer service.
Rapid Recharge
Due to our low internal resistance, Lifeline Batteries can be charged up to 20% faster than conventional batteries.
Solid Warranty
Lifeline Batteries offers one of the best warranties in the industry with our 5-year pro-rate and a one-year free replacement.
MARINE BATTERIES FOR SALE
- All
- 12 Volt
- 6 Volt
- 2 Volt
- Starting Batteries
Calculators
Which Lifeline Battery fits your needs? Use our calculators to consider power requirements, space allocation, charging protocol, weight restrictions, safety considerations and budget planning.
Marine Industry Battery Papers
The purpose of these writings is to highlight Lifeline AGM battery care and maintenance procedures. The more you learn about our marine AGM batteries and how to care for them, the less apprehension you will have when it comes to addressing your boat batteries. Topics covered will include true deep-cycle battery characteristics, best care and maintenance practices and testing / diagnosing the root of possible battery problems.
Since the information age hit sometime around the mid 1980’s, we have been bombarded with information on any topic that you could ever hope to learn about. This wealth of information has been both a blessing and a curse when trying to learn as much as you can from as many sources as you can. Self-proclaimed industry experts and just your everyday do-gooders often provide details on what to do to take care of your marine AGM batteries. Although their intentions are good, the information might be lacking in accuracies and thus turn you in the wrong direction when it comes to your boat batteries.
We are a US family owned and operated company and have more than 40 years of battery manufacturing and distributing experience. The Concorde Battery Corporation is the creator and manufacturer of the premium Lifeline AGM battery brand. The families involved work from two US manufacturing locations and a third part of the family works from two US based distribution locations. Lifeline is not a mass-produced AGM battery, but individually hand-crafted product produced using the highest quality ingredients and processes known to the industry. Our manufacturing facility is well known as a leader in the aerospace battery industry. The very same technology responsible for their success in that industry has been incorporated directly into Lifeline AGM marine batteries with the same successes. The continued growth of the loyal Lifeline AGM battery customer has caused a significant expansion of dealer and distributor networks around the world.
Unlike other battery manufacturers, when you contact Lifeline you are speaking directly to the owners and you can get answers to any technical questions. Lifeline AGM marine batteries are backed by an industry leading warranty that we support to the end.
Although there is a myriad of marine battery applications, generally speaking they can be grouped into three common categories. Yachts that rarely get used and spend most of their time tethered to shore power. Yachts that are used for coastal cruising and are used with good frequency. And finally yachts that are predominantly lived aboard and rarely on shore power.
For boaters that rarely use their vessel there are a few things to know that can help extend battery life. For starters, batteries like to be cycled (discharged and recharged) with some regularity. Most boaters have some sort of care and maintenance either being performed regularly by themselves or hired help. Periodically cycling a battery bank down between 25 and 50% SOC is good for batteries. Checking to see that all electronic equipment that will be acting on a battery bank is in good working order is paramount to battery life expectancy. If you are unable to periodically cycle your battery bank, you will need to condition charge them at some point to be determined by how infrequently that are getting cycled.
Coastal cruisers often experience some of the longest battery life-spans mostly because they are cycling and recharging batteries at optimal intervals. Lifeline recommends at the very least our AGM batteries are charged to 100% once every eight days. Doing this will prevent the batteries from slowly sulfating and ultimately suffering capacity loss leading to a shorter battery life. If you’re cruising for long periods of time and back to back days it is recommended that you regulate alternator voltage to prevent overcharging your batteries. Charger setting need to be dialed in as closely as possible to the Lifeline battery recommendations which is located on our website or accessed by contacting us directly.
Full time cruisers pose the toughest challenge for marine deep-cycle batteries and it usually comes at them from several angles. These batteries spend most, if not all, of the time NOT connected to shore power. Lifeline batteries are designed specifically to help boaters enjoy modern conveniences all while not being tethered to shore power. It is important, however, to be aware of how the batteries are being treated so you can formulate the best regimen for battery care to help extend their life. Most all full-time cruisers cannot or will not charge batteries fully and often enough to prevent them from being damaged. Boaters who fall into this category need to FOCUS on charge settings from alternators, solar and wind generators where applicable to get the most from their use. Some regimen of repeated condition charging will more than likely be required to assist in prolonging battery life. Marine deep-cycle AGM batteries were designed specifically for these types of applications, but the more you know about their limitations the better it will be for your batteries. Lifeline AGM deep-cycle batteries were specifically designed to excel in these types of applications, but they still require a baseline level attention to minimize the possibility of being without DC power.
Group 31 Battery Chemistry, Dimensions (Sizes), Weight, And Specs
The dimension of the group type is around 13 x 6.8 x 9.44 inches or 330 x 173 x 240 mm. The weight varies depending on the chemical inside. For example, lithium batteries weigh 30 pounds, while lead-acid batteries weigh 80 pounds. From the dimension, you can somehow conclude its power generation.
The BCI group 31 comprises batteries – 12V (lead-acid) and 12.8V (lithium). Sometimes, you can find group 31 lithium batteries with 24 volts and 36 volts as well. The 12V Duracell ultra is suitable for commercial equipment.
According to the BCI size classification, no specific ampere rating is given to the group. However, it’s often seen between 95 to 125-amp hour capacity. Lithium iron phosphate batteries and lead-acid batteries such as flooded cells, gel cells, and AGM are most commonly used.
Lithium Batteries
LiFePO4 battery (Lithium Iron Phosphate), possessing Battery Management Systems (BMS), is an example of the advanced chemistry and electronics combination.
The system can control different aspects of battery use, such as voltage, temperature, and input/output current, and protect it from unwanted damages. The type is increasingly popular and can be used instead of the lead-acid type in many deep cycle uses.
Compared to lead-acid batteries, the type overwhelms in many specs. It’s 2-3 times lighter, can tolerate charging cycles 5-10 times more, and gives almost the same power no matter the charging condition.
Due to its advantages, its price is more expensive. Plus, you need dedicated advanced AGM chargers or lithium chargers that support dedicated lithium charging mode.
Lithium type is used for lightweight trolling motor, RV house, security, and medical applications, which prefer weight savings and manipulate all its advantages.
Deep Cycle Batteries
It performs well when discharging at a low current, although it can’t produce a strong current. Some of the best in this category can work 20 hours in 120-125 amps hours of capacity with an RC rating of 240-250 range.
Off-grid, marine applications or electric vehicles with the highest requirements for deep discharge and cycle features are a big market for this category.
Starting Batteries
Pure starting batteries are rare in the market. Those you see that are labeled “cranking” or “starting” are actually made for dual purposes. The actual product may vary, and the actual temperature is not the same.
For example, the CCA (Cold Cranking Amps) value should be measured at 0°F, and a true “starting” should deliver a minimum of 1000 CCA. However, some manufacturers describe that their products have 1000 CCA at 32 degrees F or 68 degrees F, or even 80 degrees F.
Dual-purpose Batteries
Mostly lead-acid types with extra reserve capacity belong to this dual-purpose category. As its name suggests, it’s made with the remarkable features of two types: starting and deep cycle.
Its starting current is worse than the starting one but better than the deep cycle, and its deep cycle and deep charge features are worse than the original one but better than the starting type.
The ideal power of this type is to supply 900 CCA, 100 Ah, and 200 minutes reserve capacity at minimum. Still, there remain some exceptions to this group. For example, Optima D31M is designed lighter, thus weaker than some siblings in the same category.
Lead-Acid vs. Lithium Group 31 Batteries
Technology development helps reduce the price gap between lithium and lead-acid batteries. In turn, it makes the options between products more difficult to choose.
If you usually need to start the medium to the large engine and are looking for a dual-purpose type, then the AGM group 31 batteries are for you.
Lithium group 31 batteries are an ideal choice where lightweight is preferred. Many products of this category also can tolerate a huge number of discharging and charging cycles but produce no extra high current.
Some critical applications require reliable batteries that can supply energy even when the power fails to perform. In this case, the AGM battery is better than the lithium one. The Battery Management Systems (BMS) can disconnect the lithium type due to extremely high flow.
Conclusion
The last thing to remember is no matter what type you choose for your passenger vehicles, safety is the most important. Group 31 battery has strong circuits and can put you at risk. Ask for help from nearby stores if you aren’t confident in dealing with choosing the correct battery, pickup in-store, and other issues.
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Group 24 “Deep Cycle” 12V:
- Group 24 Deep Cycle = 75 Ampere Hours or 150Ah’s for two. (you’d need two of them for any usable house bank)
- Group 24 Deep Cycle = 350 lab rated cycles to 50% DOD
- Cost per Ah = 5000.07 For a 150Ah bank
- Cost Per Lab Deep Cycle = 97¢ per cycle – expect half the rated cycles/real world = 450.94/Cycle
Group GC2 6V “Deep Cycle” (requires two for a 12V bank):
- Group GC2 6V = 230 Ampere Hours (two 6V batteries in series = 12V bank)
- Group GC2 Deep Cycle = 850 (took mid range) “lab rated” cycles to 50% of capacity
- Cost per Ah = 450.74 For a 230Ah bank
- Cost Per lab deep cycle = 47¢ per cycle – expect half the rated cycles/real world = 97¢ per lab Cycle
In virtually the same foot print as two Group 24 12V light cycle batteries, only slightly taller, two 6V batteries wired in series for 12V will yield approximately 850 lab cycles vs. 350. It will also yield 80 more amp hours of capacity in virtually the same exact foot print. The cost per Ah, based on West Marine prices, is considerably less and the cost per lab cycle is approx half. This is exactly why the battery buying calculation must always include cycle life not just Ah to
My point here? Don’t forget to look into the lab rated cycle life and then purchase batteries that can theoretically deliver you the most cycles. We must remember that lab cycles are a theoretical best case for “real world” use. This cycle life data can be used as guidance within a brand. In other words lets stop focusing on what the “sticker” says, hell they all say “deep cycle”, and FOCUS on the expected durability of the battery in a cycling application.
Fitment of Batteries:
Unless the builder has left you no additional height at all, in the battery compartment, a GC2 6V or GC-12 golf car battery can very often fit where Group 24, 27 or 31 batteries did. A GC2 (T-105) golf car battery will fit into virtually the same foot print as a Group 24 battery only it will be slightly taller.
The West Marine Advisor – Cycle Life
Just in case you wanted to see where you can actually reference the data points am discussing, in regards to the West Marine Sea Volt/ East Penn product, you can find it in the West Marine catalog. This chart is on page 379 of the 2014 West Marine catalog.
When buying batteries for deep cycling use, always be sure you can get your hands on manufacturer cycle life data to compare their batteries across types. No data? No buy…….
Data Points: I have confirmed this data to be accurate, with West Marine, to the best of their knowledge. The data in this image comes straight from West Marines supplier, East Penn Manufacturing which is also known as Deka.
East Penn Golf L16 Chart
So what’s the bottom line between golf cart batteries (GC2), L16’s, J305’s, GC-12/T1275/J-150/9C12/921’s and light-cycling 12V Group 24, 27, 31 etc.? Below is the answer one of the largest US battery makers gave to us when we asked this very pointed question. (Source email string between Marine How To and battery manufacturer testing engineer.)
Question asked by Marine How To.com:
Q: “If the GC2, GC-12 or L16’s were cycled using the same cycle life testing as the 12V Group 24, 27, 31 etc. what would that outcome, in cycle life, actually look like? Is it fair to suggest a GC2, GC12 or L16 battery has double to triple the lab cycle life, to 50% DOD, than the 12V 24, 27 31 etc. “deep cycles” do?”
A: Senior Battery Engineer – Major US Battery Manufacturer:
“Yes, for packs of equivalent energy content (voltage capacity) the Golf Car types and L16’s are 2-3 times better than the DC automotive sizes (24, 27 and 31).”
Wow! Straight from the source, golf car batteries are 2-3X better than 12V 24, 27 31. These flooded 12V Group 24, 27 31 batteries are simply marketed in a rather misleading manner.
To make an even fairer comparison I ran the numbers on a group 24 deep cycle test and a GC2 cycle test, done by the same manufacturer. Both batteries were discharged at approximately 33% of their 20 hour Ah rating, and it can’t get more apples to apples, in terms of comparable testing, than this.
The Group 24 “deep-cycle” delivered just 350 lab cycles and the GC2 golf cart battery delivered 1000 cycles when tested exactly the same way. Both batteries were tested at the same discharge rate, to the same end of life point, yet the golf cart battery delivered 650 more cycles than the 12V Group 24 “deep cycle”.
Let’s go over some terms I’ll be using in this article:
Lab Rated Cycle Life:
This term simply denotes what the battery manufacturer see’s in their own white coat, white glove, laboratory. The batteries are cycled under ideal conditions, and quite often to no industry standardized test across brands. Some might test the battery to BCIS-02 and some to BCIS-07. Some might use the 20 hour discharge rate and some might use the 5 hour or 2 hour rate for cycle life testing.
For what it’s worth some battery makers never even conduct a 20 hour test and instead this data is “calculated” from other tests that take them much less time. The batteries which are most likely to never undergo an actual 20 hour capacity tests? You guessed it “automotive sizes” or Group 24, 27, 31 etc.types. I am quoting the battery engineer with the “automotive sizes” quote.
Battery testing procedures are guided by the Battery Council International or BCI for short. The problem is there are many different cycle life testing procedures and manufacturers rarely tell you which one they use or are testing to for the specific battery in question.
I was recently at a solar trade show and two of the big gun battery makers referenced in this article were there. I asked each manufacturer to tell me which BCI test standards they used for 12V marine G-24, 27 31 batteries vs. golf car or other deep cycle batteries. The answers I got…. BLANK STARES.
One manufacturer then suggested the golf car batteries might be tested at a 2 hour rate and the marine batteries at a different rate. If this is so then the spread between golf cart batteries and 12V deep cycle batteries can grow even wider in the real world. Ouch.
Light-cycling batteries are already half of the rated cycles of a golf car type battery and they “may” be being treated with kid gloves to boot when you actually compare testing. At a best case the 12V G-24, 27 31 battery might be half the cycles of an actual deep cycle in the lab but they may actually be worse than half the rated cycles depending upon the testing used hence the battery engineers statement of golf car type batteries being 2-3 times better for cycling use.
This is just a sampling of some BCI Tests:
- BCIS-05 – Capacity Testing of Electric Vehicle Cycling Batteries
- BCIS-06 – Constant Current Cycle Life Testing of Deep Cycle Batteries
- BCIS-07 – Cycle Life Testing of Batteries for Golf Carts
- BCIS-08 – Cycle Life Testing of Deep Cycle Marine/RV Batteries
What tests were used, and the differences between these tests, can result in massive variances, brand to brand, and also in their cycle life claims. This is why it is nearly impossible to use lab cycle life data across brands or manufacturers. Through in-house testing battery manufacturers can produce cycle life data across their own products, based on their own testing.