Industry Article

How long does a Fullriver AGM battery last?

Not all AGM batteries are created equal.  The difference between a Fullriver AGM and Brand X is often worlds apart.  From the purity of the lead, or the thickness of the plates, to the extra time invested in the plate curing process.  So, today we’ll talk about what we know on an intimate level, Fullriver premium AGM batteries. 

Context, Context, Context.

How long?  A question that humans have been asking seemingly since the beginning of time.  How long will I live?  How long until I can retire? And of course, the ubiquitous, “How long until we get there?” Questions like these are best answered by looking at the specifics of each situation.  How long will I live?  This largely depends on where and how you live and some good luck with your genetics.  How long does an AGM battery last?  While Fullriver batteries have a 10-year design life, this must be put into context with several factors.


First, let’s talk about usage of the battery.  Any battery has a finite amount of energy it can give over its lifetime. If every time the battery is used it is drained completely, the amount of time the battery will last is less than if the battery was used moderately and then recharged. 

Golf is a good example application to better understand the concept.  Batteries used to play two to three rounds of golf before being recharged will not last nearly as long as a set of batteries used to play one round of golf before being recharged. The amount of energy removed from a battery is known as Depth of Discharge (DoD).  Fullriver’s Cycle Life vs. DoD chart is a great reference for understanding the impact of battery usage:   

Graph Pictured for Fullriver DC Series Batteries

We can see from the above chart how widely cycle life can vary based on usage.  If every time the battery pack is used, it is discharged fully to 100%, we can expect ~450-500 cycles.  Conversely, if only half of the usable energy is discharged, the cycle life will be somewhere around 1000 cyc

We could further discuss the impact that the rate of discharge has on the batteries (i.e., how fast the energy is removed from the batteries), but let’s keep this at a 30,000-foot view.  Suffice it to say that the lower the energy demand on the battery, theoretically, the longer the usable life of the battery will be.


Charging is the fuel of a battery.  Just like automobiles, high quality fuel produces the best performance and longevity.  Charging batteries properly is perhaps the most important aspect of ensuring a set of batteries lasts as long as possible.  A reputable charger should be used that includes an actual AGM setting.  Avoid chargers that claim to charge any battery type using one generic algorithm.  Additionally, the charger should at a minimum put out at least 10% of the battery’s rated capacity in amperage, but ideally the output will be closer to 25% of the rated capacity.  Look for a charger that approximates our recommended voltage for each phase of charging.

A note about PSoC

It is critical that the batteries are not left discharged for long periods of time between usage, commonly referred to Partial State of Charge (PsoC). This does not mean that the second a battery has been discharged it must be recharged immediately, but it does mean that a battery should not sit for days until it is recharged.  If battery usage is light, a complete, uninterrupted charge once a week should be sufficient.  For heavier use applications, a complete charge cycle may be required daily.


Not too hot, not too cold, but just right.  Of all battery chemistries, AGM batteries are documented to perform the best in the cold. While all chemistries suffer temporary capacity loss in the cold, AGM seems to fair the best when compared to lithium, flooded, or gel batteries.  On the other end of the spectrum is, of course, heat.  For any lead-acid battery, heat degrades cycle life.  Specifically, every 12°C (22°F) over 25°C (77°F) can reduce battery life by as much as half. The Fullriver cycle life graph is based on cycling at a constant 25°C (77°F). In the real world, temperatures fluctuate by season, and even between night and day. 

The right tool for the right job

Just like using a screwdriver that is one gauge too small or large can create frustration, and a stripped screw head occasionally, batteries are designed to tackle specific needs.  Using an automotive starting battery to power a golf cart would be disastrous. But the design specification is even more tightly focused when it comes to deep-cycle and dual-purpose batteries. 

Deep-cycle batteries like the Fullriver DC or EGL Series are designed to run a purely electrical application until their energy is depleted and then be recharged.  They were designed to do this process on repeat, discharge, recharge, and so on. While they can start an engine reliably, this wasn’t part of their design intent.  Plus, they can be more expensive when the extra cost may not be warranted.

Dual-purpose batteries like Fullriver’s Full Throttle series are a hybrid in that they are very capable when starting an engine, but they have a specialized grid design (Thin-plate, pure-lead) that also allows them to do some cycling. Full Throttle excels in applications like marine where they serve to start the engine and also need extra capacity to keep instruments running, especially with the engine off for short periods.  For pure cyclic applications like mobility, they just won’t have as long of life as a true deep-cycle battery.

We can see that there are many factors to consider in predicting the life of a battery. Starting with the highest quality battery, and accounting for usage, charging, climate, and the needs of a specific application are all relevant to determining how long a battery is going to last.  With all of these factors optimized, we can expect battery life to go on long after the manufacturer’s warranty has expired.

We want to hear from you! What has your experience with battery life been? How are you maximizing battery life?

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23 comments on “How long does a Fullriver AGM battery last?”

  1. Hello –

    Please call me regarding FullRiver Group 31 AGM battery warranty.

    Mark Rinker
    Seattle, WA

  2. Hi I have bought a yacht with four fullriver dc120-12 12v120ah/20hr
    Cyclic application batteries that are all completely flat for possibly two years is there any chance of them being useful again
    I’m in Australia

  3. You didn’t quite address the issue of how long? I expected you to offer various use cases and suggest estimated life spans for each use case. Also, you didn’t shed light on the battery C-rating, which is a very important consideration when dealing with the subject of how long.

  4. Hi, Marc.

    Can you define flat? What voltage are they sitting at? Unfortunately, that may not matter, sitting uncharged more than 12 months they are most likely unrecoverable.

    If you’d like to source a replacement set in Australia, check with R&J Battery.

  5. Awi,

    I’m sorry you were disappointed with the content. This type of article is not meant to be a white paper or an exhaustive exploration of the topic, but rather an introduction for a larger audience to consume at more of an entry level.

  6. I have the HC80 in my campervan. Installed by an official camper builder (RollerTeam). I use it as a daily car, so i has never been depleted and always charged. I just lasted a bit more then 3,5 years. Is this a normal age? It has never been depleted. Never been overcharged.

  7. Stijn,

    Was the HC being used as a deep-cycle battery or only for starting? If you were using it as a deep-cycle battery, what was it being recharged with?

    With all of the variables present in any one application, it’s hard to know how long something could or might have lasted. We have users with many different experiences. However, if the battery was active for 3.5 years, you can be certain the failure was not due to a defect. These would have manifested much earlier in the life of the battery. So, probably something specific about usage contributed to this.

  8. Looking at your chart, if I discharge to 80% I can do this about 700 times. If I discharge to 40% I can do this around 1400 times. In both cases though I would have delivered the same number of Ah. For example a 100Ah battery cycled at 40% x 1400 times delivers 100 x 0.4 x 1400 = 56,000Ah over the life of the battery. Likewise, a 100Ah battery cycled at 80% x 700 times delivers 100 x 0.8 x 700 = 56,000Ah. How am I better off discharging to 40% rather than 80% when both deliver the same output over the life of the battery.

  9. Correct, Glenn. When people look at these charts, it’s typically for reference for comparing their habits vs the amount of life they can expect out of the battery. In the case of an application like off-grid solar, customers want their banks to last a certain amount of time, so they will build it to a size that keeps the discharge to a point where they don’t have to replace the bank as often.

  10. We had our custom built caravan built in 2013 had full river AGM X2 installed and they are still going. We leave our compressor fridge on and never have had a problem. We live in our van and travel around Australia. We have 2 x 120 solars panels.

  11. Grant, thank you so much for your comment. We love hearing about people really getting out there and using these batteries! Would you be amenable to emailing us some pictures? You can send them to

  12. These batteries are worth their weight in gold! Mine were bought in 2012. A 105ah which has spent its life under the bonnet which just now is up for replacement. Pretty impressive for an agm under the bonnet! My 120ah lives in the back of the car and still has 100ah+ capacity and going strong. I wouldn’t buy anything else.

  13. Could you add a chart to this with percent discharge vs. voltage? The battery meter reads in volts not DOD so not sure from this what voltage I should set an auto start generator to preserve battery life in my off grid system (24 ea, 2V, 1150 ah)

  14. hi my name is david ilive on a 70 foot narrowboat in the uk , i have 5x200ah agm fullriver batteries on board for leisure and cranking purposes, i have just had a look at the code on the batts to try to work out the age as i have only had the boat 4 years,the code is k40225 a , surely these batteries cant be nearly 20 years old or will it mean 2014 ?

  15. I have (2) group 31 8d 260 12v on my sailboat. They are now 2 years old, but have had this issue since the first few months. Charger is a new Magnum Energy, set up for AGM. I leave the dock after weeks plugged in, fully charged. One day of combined Sailing / Motoring, I drop the hook for the night. The only draw is LED anchor light, few reading lights and refrig / freezer total- 6-9 amps (I can see it on the panel). 10 hours later in the morning I am down to 12.2 volts / sometimes less. With 520 Amp hour capacity how can I possibly be that low with only 100 amp hours +/- of use? Worst Case a few weeks ago after 10 hours sailing lost all electronics with completely dead batteries!

  16. Dan,

    Please send us an email so we can correspond more directly. warranty at fullriverbattery dot com

    Thank you,

  17. Hi

    We live on a sail boat. Our first set of Full River AGM deep cycle batteries lasted an incredible 8 years. We live at anchor so they were discharged and recharged every day. Quite incredible!

    We are currently traveling in the tropics. Unfortunately the batteries are installed in the engine room and it’s bloody hot in there.

    What is a reasonable temperature limit? They are currently at 52 degrees C. I have removed the engine covers so I’m now slowly cooking my family. All our charging systems are temperature compensated.


  18. Hi, Mark.

    Great to hear about your experience with our batteries!

    The general rule is every 5 degrees over 27C reduces overall cycle life by 20%. If at all possible, you’ll want to figure out a way to cool the battery room down. 52C is incredibly hot and almost certainly will have a big impact on the life of the battery pack. I know that’s not great news for you, but it is the reality.

    Let us know if we can help with anything.


  19. I have had hc44 battery in my 94 Honda civic for 3.5 years. I haven’t started the car in the last 6 months, I tried starting the car and the battery was dead. I put a volt meter on it and it has 1.2V. Is the battery already dead?

  20. Connor, unfortunately, it sounds like you had a parasitic draw from something in the vehicle while the car sat. At 1.2V the battery is far beyond recovery and it will need to be replaced.

    If you are going to store the battery in the future, after it is charged up, simply disconnect the negative cable from the battery to prevent this.


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