Winter Care for AGM Batteries?

Gherzig

Winters are long and cold in upstate NY.  My 400 is stored outdoors with a cover.  What is the best practice?
-Plug into shore power continuously all winter
-Top off batteries with shore power occasionally (monthly?)
-Let them sleep all winter
My inclination is the occasional top off but I am not certain that is what is best.

pthomas745

Fully charged, battery switch off, and they will hold a charge for months.  Nothing else needs to be done.  An occasional trip over to the trailer, a few minutes with the Victron app to check the voltage (which will show you how long a fully charged battery can hold a charge). 

Either of your other methods will also work.  But...there will come a day when the trailer needs to sit for a while without shore power available.  If you see for  yourself how long the battery (switch off!) can hold a charge, you can let it sit and be comfortable with that choice.

manyman297

Also, depending on if there’s snow on my cover or not, I’ll still get a bit of a solar charge to the batteries which is never a bad thing. About as maintenance free as it gets.

bergger

Last winter I just let them sit and as mentioned by others we did get just enough solar through the trailer cover to keep the batteries topped off.  However this year we have had and extremely cold November and December.  Negative temps and single digits are the norm.  Heck this Thursday the high temp will be 0 degrees.  Several weeks ago I noticed that when I would check the batteries through the victron app that the solar controller would be turned off most of the time.  On a rare warmer day it would turn itself back on.  It's my assumption that it is just so cold the controller is shutting itself off.  For this reason I have decided to keep it plugged into shore power for the winter.  

YanniLazarus

I understand that lithium batteries need to be relatively warm to be safely charged. I wonder if it can harm an AGM battery to be left on a smart charger through freezing winter months.  Apparently there are optimum charging temperatures- even for AGMs. We use our 320 occasionally during the winter and like to have our batteries fully charged and ready to go.  I'm wondering what the best approach is for winter AGM management.   (In the past I've left my smart charger on all winter.) Don't suggest this old man carries those crazy heavy batteries inside if you want to be taken seriously! 

pthomas745

A fully charged lead battery won't freeze until -80F.  Lithiums should not be charged if the battery itself is below 32F, but they can be safely used like any other battery.  (There are many strategies to keep a lithium battery warm...and the batteries themselves will also produce a bit of heat as they are in use.)

It gets a little confusing, but there is lots of info here about the various charge rates at lower temperatures.  A lead acid battery is very forgiving on charging at low temperatures.

https://batteryuniversity.com/article/bu-410-charging-at-high-and-low-temperatures

Deb55

We have a 2018 T@B 400 with the original 2 6-volt AGM batteries. I fully charge them before putting on the cover, and turn off the battery switch. So far, this has been fine for the winter here in central Massachusetts. We had a victron battery monitor installed, and I check it every couple of weeks. Plus, as others have mentioned, it's still charging some through the cover. I haven't had to plug in yet over the winter.

MNtabernacle

We have a 2018 400 with the big 12 volt AGM, living north of the Twin Cities, and have had lows in the -40's over the winter. We top off the charge, turn off the switch and let it rest outside November to May, and when we wake it up it is still raring to go.