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What happens if a AGM battery is charged too fast?

ianganderton

Auckland, NZ
Joined
Nov 8, 2019
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Auckland, New Zealand
So I was reading a product manual (wild n crazy life I lead) and saw a maximum recommended charge rate for lead acid of 0.2C

Is this a good recommendation?
What happens if that is exceeded on a long term basis?
What is typically the maximum charge rate lead acid batteries will actually accept?

If someone had a campervan with a solar charge controller that was rated to deliver 0.2C and an AC to DC charger that could also deliver 0.2C and the battery was at approx 50% charge what would occur?
 
If that's from the battery manufacturer, yes. AGMs tend to accept higher charge rates than FLA or gel. If it's from a charger manual, it's probably a guideline. It's probably reasonable.

I lumped them together in my other post for convenience, but I did note that they are more forgiving or tolerant.

At lower SoC, they are even more tolerant. Charging is also self-limiting. When they hit their absorption voltage, they start tapering current. 0.1C at the absorption current is about 80% SoC, so you'll never exceed 0.1C above 80% SoC, so there's a little safety built in.

Higher current charging will have a negative effect on cycle life. How much? Very hard to say. .25C vs. 20C, probably not something someone would notice except they might have had to replace their batteries a few months earlier than had they kept it to 0.2C.

There are guidelines and there are battery manufacturer's specifications. Always follow the manufacturer's specification.

As a giggle point, for "other" purposes I shove 300A into a 950Ah (about 0.3C) FLA 12V bank at lower SoC, and yanking 150-200A out of them afterwards. I've been doing that for two years several times a week. They're still doing well. After a few months, I can tell they're getting a little less responsive, but a few equalizations every year seems to restore prior performance.
 
AGM have slightly higher charge efficiency then regular flooded lead-acid but it is a sealed case and electrolyte staved design. Electrolyte is just saturated in glass mat so there is no reserve above plates. It is a close cousin to Gel cells which hold electrolyte in gel.

At less then about 13.5v they can take a higher rate as little gas is created. They have a safety vent but you don't want to have to use it. Too high a charge rate will cause too much internal pressure from hydrogen and oxygen gases causing the safety vent to release pressure. Normally small amount of gases are recombined without loss to venting. If you vent you lose water from electrolyte that is not replaceable due to sealed case.
 
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The limiting factor on most lead acid batteries is internal resistance and voltage rise. What I mean is I can hook a 50amp charger to my 50% depleted battery but the charger only charges at 35 amps. Why? because the only way to force more amperage into the battery is to bring the voltage even higher, beyond what is recommended.

In the AGM world I’ve had the best long term luck with odyssey batteries. Ran them for many years, have had no sudden failures. There literature says you can charge at any rate as long as temperature and a set voltage (14,8 I think) is not exceeded.
 
I've bought literally tons of lead acid batteries over the past decade. Which makes me an experienced student I guess. I am currently buying LiFePo4 because I expect them to sit ~ four years before use - I'm a prepper and slightly pessimistic but I digress.

Lead acid characteristic vary about as much as you can imagine. Deep cycle batteries can take a higher charge rate. As can bigger batteries and most quality batteries. Then we have forklift batteries - built to handle extreme abuse and still last 10-20 years or so. Mine is about 10 years old I think - bought it used and neglected.

I might have stayed with lead but I seek sustainability for over a decade. I generally do not recommend following that path. It is too expensive and space intensive. Then again - the system is cracking. But I digress.

Deep cycle/solar batteries can generally take a pretty high rate of charge. Shoot, your car and especially your trucks alternator often delivers a high rate of charge.
 
For a prepper, lead acid (FLA) is the best.
without the acid in it (dry) , you can shelf them forever.
and they are ready in a few minutes.
you can charge a LFP fast, that is not the problem , the problem is if this is a high capacity battery, finding enough current on a short time could be a problem.
The best in that case is to set up a solar system, keep the battery charged at 70%..
The panels will last 20 years, the battery probably a lot less.
Even without battery you will get electricity with panels.
 
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For a prepper, lead acid (FLA) is the best.
without the acid in it (dry) , you can shelf them forever.
and they are ready in a few minutes.
you can charge a LFP fast, that is not the problem , the problem is if this is a high capacity battery, finding enough current on a short time could be a problem.
The best in that case is to set up a solar system, keep the battery charged at 70%..
The panels will last 20 years, the battery probably a lot less.

Last time I was able to buy dry lead acid batteries was decades ago. LFP stores best at ~ 40-50%.. Best range is 40% to 80% for cycling purposes.

The panels will always produce. Wind born abrasions to the glass slowly reduce their efficiency. Conservatively cycled LIFEPO4 can last for decades - if the BMS does not fail.
 
The limiting factor on most lead acid batteries is internal resistance and voltage rise. What I mean is I can hook a 50amp charger to my 50% depleted battery but the charger only charges at 35 amps. Why? because the only way to force more amperage into the battery is to bring the voltage even higher, beyond what is recommended.

In the AGM world I’ve had the best long term luck with odyssey batteries. Ran them for many years, have had no sudden failures. There literature says you can charge at any rate as long as temperature and a set voltage (14,8 I think) is not exceeded.

I can relate to the Odysseys and other pure-lead agm's. In fact, that is what got me started long ago with solar, when I found out that I could hammer these with like 1C current - which might be important in winter, or northern latitudes where true solar-insolation hours might be very short.

But pushing 1C into your typical Odyssey / Optima or other pure-lead can be expensive from a panel-cost standpoint. But it is sure fun to watch them charge in say 2 hours roughly at .5C and then the sun goes down. $$ but maybe the only way to do it in London or Stockholm.

I've even used the pure-lead little Cyclons for smaller solar projects that were only exposed to very little sunlight with appropriately large panels to accomplish the job. Hilarious to look at.

Pure-lead high-rate charging is what got me going, and then LifeP04 was a very natural transition!
 
.2C seems fine for flooded. For AGM I put .2 as a minimum. AGM actually likes to be charged heavy and fast. Slow charge is the death of AGM. Keep the voltage in spec and you are fine. If you find yourself thinking you are charging too fast.... the battery is too small.
 
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