How to properly maintain AGM batteries during the winter

[john61ct]

Originally Posted by 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.

Yes, a charge source that only puts out just enough to counter the bank's self-discharge can be a great solution.

But you are trusting it doesn't fail. . .

[jen1722terry]

good thread.

We have three Odyssey AGMs on our sailboat, which is stored in coastal Maine each winter. The MFR recommends fully charging them and leaving them on the boat, fully disconnected. We've done this for four winters and, so far, the batteries are fine.

We also own an Odyssey charger , which we use each spring and fall to do a reconditioning charge on each battery.

Not sure about Lifeline, Firefly or other AGMs.

Jenn and Terry

[Srah 1953]

In the book the "12V Bible" the author says that leaving a battery on a trickle charger for an extended period is even worse for it than to be left lying around unused for a whole winter.
Personally, I have no idea.

[hellosailor]

While AGM makers usually say the batteries can sit for six months with zero maintenance and zero damage, keeping them on a trickle charger is still more likely to prevent any sulphation.

There are a number of inexpensive ones (NOCO and CTEK) that can be found online, which actually evaluate the battery, set specifically for AGM, and then over the course of a week they will ensure it is topped up and then kept in a light maintenance mode indefinitely after that. Some models will do two batteries at once, some are cheap enough so that you could just buy one for each and keep them redundant.

Unlike the dumb "tenders" they don't just rely on random chance, they won't cook the batteries.

[CaptainMCT]

And always Keep them off the ground, right?

[hellosailor]

MCT, that was an important point when batteries came in hard rubber cases, before the days of plastic. And "the ground" was an unheated slab floor, that allowed the battery temperature to pull down and freeze.

So forget about that one, worry more about letting them freeze, on or off the ground.

[CaptainMCT]

Thanks! Also, Should maybe be important to mention hear also that if you’re in a place where you’re worried about it freezing, to sail south! happy sailing all!

[sailinglegend]

Originally Posted by MJH

--------I'm not an electrical engineer but this doesn't sound correct as this happens every morning not just during winter storage. ....

I'm afraid you have completely missed my point!

When a solar charger - or any other type of charger - turns on or gets turned on when the batteries are already 'fully charged' and there are no loads on the batteries, then that will raise the voltage to 14.4v or above until the charger's algorithm turns the charger off. This is overcharging the batteries.

Most chargers go into a fixed charge time of say 2-3 hours, some 'smart' chargers may modify this time depending on how long it takes to get to 14.4v.

For example my Victron mains charger stays at absorption voltage for 5 times the duration it takes to get to 14.4v. So that would be 5 hours if it takes 1 hour to get to absorption. If it takes 30 seconds to get to absorption it stays there for 2.5 minutes.

[jen1722terry]

Hello again to all.

One thing we learned about AGM batteries is that the absorption voltages can vary among manufacturers. For example, our Odyssey AGMs have an absorption voltage of 14.7 volts, while other manufacturers may have a different absorption voltage. This is a good reason to use a programmable smart charger to charge and maintain your batteries. If you're using solar, you'll need enough solar capacity (in unshaded watts) to maintain the required voltages for sufficient time to fully charge your AGMs. It can get a bit complicated, and those of you who are still a bit confused have our sympathy. We went through the AGM learning curve when we replaced our old AGMs that came from the prior owner with a different manufacturer and learned that our solar controller had to be replaced and also learned that our solar panel was too small.

We're planning to add more solar capacity this spring, and any advice on suppliers, manufacturers and local installers in mid-coast Maine would be most appreciated. In the meantime, we run our portable smart charger dock-side a few time each summer to de-sulfate the batteries.

Of course, this thread begs the question: "why AGMs at all?" For us, winter storage in-boat without supplementary charging gives us more storage options for our boat at lower cost. Also, our boat is smallish (31 feet) and an older, narrow design (beam 9'9"). She's stout, but can really roll in a beam sea and we don't want to risk acid spillage. Lastly, the PO moved the batteries from their cockpit locker location to a custom rack under the cockpit sole. This moves the considerable weight lower and centered over the keel, a good thing, but makes it harder for us to access with aging backs and vision issues. Never have to check or add water, but we do have to check cables and clean the battery tops periodically which I do with plastic tools, headlamp and a mirror.

Windy up here in Mahone Bay, Nova Scotia this morning. Large seas running even in our sheltered inner harbor out front of our house. The local lobster fishers may have to delay their Friday start of their quite-profitable winter season if this weather keeps up.

BTW, we rent our house here for summer weeks. It has a fabulous harbor view, a long pier with float and and we can even throw in the use of our mooring, rated for 10 tons.

Cheers!

Jenn and Terry

[a64pilot]

Originally Posted by Srah 1953

In the book the "12V Bible" the author says that leaving a battery on a trickle charger for an extended period is even worse for it than to be left lying around unused for a whole winter.

Personally, I have no idea.

That is correct, reason why is even a trickle charger, is a charger, meant to charge a battery.
You don’t want a Charger, you want a maintainer something that maintains SOC and doesn’t charge.
Problem with that is nearly every battery manufacturer has a different float voltage, so you need one that is adjustable, to .1V.
Then it also needs to be temperature compensated, so that in cold weather the voltage is increased and decreased in warm wx.

Now we are talking $$ unfortunately, especially for just two batteries.

I still say leave them disconnected and every month or two check open circuit voltage and charge if you think necessary, or be prepared to spend some money, which I couldn’t justify for two batteries myself.
Plus we are assuming 6 months, is Winter really that long?

[thinwater]

Originally Posted by a64pilot

...Plus we are assuming 6 months, is Winter really that long?

You would be staggered by how many boats only sail from Memorial Day to Labor Day. Maybe a few more weeks on each end.

[George DuBose]

I use a BatteryMinder charger that is a pulsing charger and is supposed to desulfate AGM batteries.

Avoid Battery Sulfation with a Desulfating Battery Charger | BatteryMINDers

I am running 10 years on my Optima Yellow Top Series 31s. After the house bank was flattened a couple of times, I became concerned about sulfation and found the BatteryMinder.

I leave the batteries in my storeroom on the charger all winter and so far so good.

George DuBose

[Captain Bucknut]

a couple pennies here.....

I recall reading Maine Sailor did a test by leaving a battery in his shed outdoors during a Maine winter with no short term harm. Not sure where he is on the long term end of things....

I'm in the camp of putting them on a charge initially to allow them to fully charge. I test mine first and record the battery level. Run them through a charge and check the level again and record. Recheck in a couple weeks to verify that they hold a charge within a couple points. Then I forget about them until its time to pull the boat out of storage. Test and record. Recharge, test and put em in the boat for the season.

Make sure that you have them off the floor in the basement especially if the floor is concrete. That floor will typically be at ambient ground temper of 55deg F or below and will suck the life out of the battery.

This has worked for me for me for the past couple of decades of RV and SV uses and this is how my Dad did so previously. The only time I've had to replace a battery prematurely was due to my own negligence, not from following a tried and true method.

That's my $0.02.

[Eder]

The AGM's (not Lifeline) in my rv have spent 10 years being stored 6 months at a time just disconnected. This includes winters in Alberta...temperatures drop as low as -40. So far no issues although my 500 AH house bank has lost a bit over the years.

[john61ct]

Originally Posted by Captain Bucknut

Make sure that you have them off the floor in the basement especially if the floor is concrete. That floor will typically be at ambient ground temper of 55deg F or below and will suck the life out of the battery.

Again, as above, no longer true wrt concrete.

And 55°F or below is ideal for storage, untill you get to negative numbers.

Heat kills batteries, cold helps longevity.