How to properly maintain AGM batteries during the winter

[cburger]

Have a couple of AGM batteries that I've taken off my friend's boat brought into the basement for storage and want to make sure that I am maintaining properly. These are sealed so no way to use hydrometer on them. Can the members recommend a proper procedure for this as well as a quality brand trickle charger to help keep in peak ccondition.

[Eder]

If storing for 6 months after a full charge nothing needs to be done.

[a64pilot]

A quality trickle charger doesn’t exist, or I have never seen one.
Any quality Charger, the voltage is controllable to .1V or better.
I’m in the camp of fully charge them, store them in a cool, not freezing cold environment and leave them alone.
If you still worry about them, then monitor their resting voltage and recharge if it drops much, much is I think a volt.

[john61ct]

I also believe storing cool and isolated is safer than hooked up to Float on even a top quality charger.

However if a large expensive bank, six months is **way** to long, longevity will be affected.

Charging overnight once a month should be fine.

Personally I'd do it every 2-3 weeks if not inconvenient.

If monitoring the charge with an AH counter shows self-discharge is under 1% during that time, then can add a week to the interval, and so on, until you're topping off around that much each time.

If all this is just not possible then keeping on Float with a top quality charger, properly adjusted.

But someone trustworthy should at least be checking on them.

If the bank is only worth a few hundred then obviously less concern is warranted, and in the end, Up to You!

[a64pilot]

As a reference a Lifeline battery kept at 77F will self discharge at 2% per month, IAW the Lifeline manual

[john61ct]

Yes that would be an extreme case, would probably go with Floating if I couldn't find a spot much cooler than that.

[john61ct]

Also note the mfg specs are When New.

Older units need better care, more susceptible to PSOC abuse.

[sailinglegend]

Lets be very clear - AGMs are not very different to other Lead Acid batteries. Yes they may have a lower self discharge that a Flooded Lead Acid battery, but 2% per month for 6 months is too long to leave them. They will suffer from PSOC, Partial state of charge, and that means sulfation will cause lead sulfate crystal to harden on the plates which cannot be removed 6 months later.

Leaving FLA batteries on float for 6 months is the least worst option because they need an absorption boost maybe every 7 days to stir up the electrolyte and stop acid sinking to the bottom. Some smart chargers can do this automatically. This doesn't happen in AGMs.

If you leave batteries on a boat then the best option is to use solar, but cover some of the panels to limit their output current and change the controller settings.

The problem with solar is that at night the controllers turn off, but first thing in the morning they will start charging at absorption voltage on batteries that are probably full anyway, especially if all DC circuits are switched off. The charge controllers don't know the batteries are full charged so may stay at their pre-set absorption time of maybe 2-3 hours, before dropping to float. This will be overcharging the batteries, that means staying at too high a voltage for too long, doing this every day for 6 months will dry them out.

One solution is to change the Charge Controller to a lower absorption voltage of say 14v to stop the batteries gassing above 14.4v. It's battery gassing when batteries are fully charged that does the damage.

[john61ct]

Originally Posted by sailinglegend

If you leave batteries on a boat then the best option is to use solar, but cover some of the panels to limit their output current and change the controller settings.

The problem with solar is that at night the controllers turn off, but first thing in the morning they will start charging at absorption voltage on batteries that are probably full anyway, especially if all DC circuits are switched off. The charge controllers don't know the batteries are full charged so may stay at their pre-set absorption time of maybe 2-3 hours, before dropping to float. This will be overcharging the batteries, that means staying at too high a voltage for too long, doing this every day for 6 months will dry them out.

One solution is to change the Charge Controller to a lower absorption voltage of say 14v to stop the batteries gassing above 14.4v. It's battery gassing when batteries are fully charged that does the damage.

YES

If the target bank is isolated from all loads, then just setting Absorb to the desired Float V is a more thorough workaround for controllers with such limited intelligence.

[CaptainJohn49]

Just a side note, I used to have a dump truck and take the batteries out every winter to store in the basement. I was advised to never store them on the concrete so I had a short 2 x 12 that I set them on. The batteries lasted as long as I had the truck which was about 10 years. They were lead acid but I think the same advice would go for AGM.



CaptainJohn49

[MJH]

Originally Posted by sailinglegend

Lets be very clear - AGMs are not very different to other Lead Acid batteries. Yes they may have a lower self discharge that a Flooded Lead Acid battery, but 2% per month for 6 months is too long to leave them. They will suffer from PSOC, Partial state of charge, and that means sulfation will cause lead sulfate crystal to harden on the plates which cannot be removed 6 months later.

Leaving FLA batteries on float for 6 months is the least worst option because they need an absorption boost maybe every 7 days to stir up the electrolyte and stop acid sinking to the bottom. Some smart chargers can do this automatically. This doesn't happen in AGMs.

If you leave batteries on a boat then the best option is to use solar, but cover some of the panels to limit their output current and change the controller settings.

The problem with solar is that at night the controllers turn off, but first thing in the morning they will start charging at absorption voltage on batteries that are probably full anyway, especially if all DC circuits are switched off. The charge controllers don't know the batteries are full charged so may stay at their pre-set absorption time of maybe 2-3 hours, before dropping to float. This will be overcharging the batteries, that means staying at too high a voltage for too long, doing this every day for 6 months will dry them out.

One solution is to change the Charge Controller to a lower absorption voltage of say 14v to stop the batteries gassing above 14.4v. It's battery gassing when batteries are fully charged that does the damage.

--------------------------------------------------------

I'm not an electrical engineer but this doesn't sound correct as this happens every morning not just during winter storage. My Gel batteries are now 14 years old being solar charged the last three years non stop and I haven't seen or heard of any need to do this...it doesn't make any sense to me.

To my thinking a very basic understanding of solar charge engineering is that it is only going to work during daylight hours and that has to be factored in...I would think a smart charge controller would take care of it.

I would welcome some electrical engineering expertise into this discussion to clarify this particular question of solar charging.

~ ~ _/) ~ ~ MJH

[sailortype]

the concrete floor thing is a myth dating back to when battery bodies were made of bitumen impregnated cardboard and would leak out to the concrete. Modern battery casings are not susceptible to this. The wood might keep them a few degrees warmer but not sure that is a benefit of any kind.

[waterman46]

We left our AGMs connected to a small solar panel in LaPaz all one summer, about 9 months total and no problem. Batteries were just fine when we returned to the boat. I oriented the single solar panel so it would receive only a small amount of sunlight each day, and tested it so that it would output about 1 amp max for a few hours a day. Using a cheap solar regulator.

[john61ct]

Originally Posted by CaptainJohn49

I was advised to never store them on the concrete so I had a short 2 x 12 that I set them on.

no longer necessary for many decades

leftover from before batt case materials got vastly improved

[john61ct]

Originally Posted by MJH

My Gel batteries are now 14 years old being solar charged the last three years non stop

There is a huge distinction between how a charge source should behave during normal cycling usage, while the bank is connected to loads, and

while they are isolated and in storage.

Very few regulators / controllers have much intelligence as to their settings / algorithms like Absorb Hold Time and Absorb Return.

It is up to the owner to verify charge sources are doing what the mfg specs for a charge profile, measuring with a known good ammeter/DMM or ideally an AH counter.