Batteries, Winter, & Nebraska Cold

[Jonathan M. Cohn]

I would like to charge my boat batteries, disconnect them from everything but each other, and leave them in the boat stored in a non-heated storage unit garage. They will get cold. I have no electricity in the storage unit. I would hope to leave them until spring. The batteries are West Marine AGM, Group 27, 92 amp hour batteries.

 

I have read some people say this is fine and others say I must find a way to charge or trickle charge them. Thoughts? I am looking for the wisdom of the group.

 

[Don Silsbe]

I remove mine for the winter, and I understand that’s not an option for you.  My recommendation for you is to go to a Camping World, or other RV dealership, and ask them how they manage all the batteries in their onsite inventory.  Go straight to the desk where they schedule service, and ask them.  
 

If I were you, I’d charge them fully before storing, and check the battery voltage periodically through the winter.  When one gets low, you’ll need to bring it home for a charge.  But find out what the big boys do with all their batteries out in the Nebraska winter.

[messingdd97]

As long as they're fully charged, you should be ok.

 

https://www.usbattery.com/preparing-deep-cycle-batteries-for-winter/

[Jonathan M. Cohn]

I fully charged the batteries and switched the battery selector to off. The solar charge regulator may still draw a tiny bit of electricity as it monitors battery voltage. I am going to check the boat regularly to see how the voltage changes. If the batteries get lower than 12.5 or so,  my plan is to use the on board 12v battery charger with AC provided from either my vehicle's built in inverter or an external power station with 600w inverter. If all else fails, I'll tow her back home to the garage to charge.

[Don Silsbe]

That’s a good plan, Jonathon!

[Captain Tim]

A charge controller does have a draw. Fine your draw, multiply by 24. Multiply that by number of days the boat will be stored.

Subtract that number from 92 (your battery) if the number that is left is low pull the battery put it in your garage and keep an eye on it. 

[Captain Tim]

By the way, I only gave you my 2 cents so I would get points towards my next merit badge.

Have a Great Thanksgiving!!!

[Paul356]

I've been leaving mine in the boat all winter, lead wires disconnected, ever since I saw the boatyard was storing the batteries it removed in an unheated area of the shed.  Seems fine.  I fully charge before leaving them.

[Hirilonde]

When the mechanics at the full service marina I worked at winterized boats they charged the batteries and diisconnected them from everything. These were mostly sailboats and up to 70', with multiple batteries of all types.

[Jonathan M. Cohn]

I actually have three 92 amp batteries. I'll report back next week on how they did. The batteries provide 1/2 the ballast in place of part of the water ballast.

[Hirilonde]

17 hours ago, Jonathan M. Cohn said:

I actually have three 92 amp batteries.

92 amp hour battery, aka group 27.

[Don Silsbe]

Hirilonde is telling you that your terminology is incorrect.  Your batteries each have a capacity of providing 92 hours of electricity at a load of one amp.  If you had a 92 amp load, something would melt, catch fire, or explode.

 

I just did some research for my own benefit, which I want to share.  AGM and flooded batteries should never be discharged to 50% of capacity. Going below 50% reduces the life of the battery.  What is 50%?  That was my question!  The answer is simple— 12 volts.   If your voltage dips below 12, you’re shortening their life.  The numbers are completely different for an LePO4, but lithium batteries are lighter in weight.  For your application, you want the weight.

 

So, when you check those batteries this winter, and the voltage nears 12.0v, bring ‘em home to charge.

[Hirilonde]

The 50% thing is very important.  By the way, your batteries should be fused within 12" of the battery itself on the positive side. The size fuse is based on the gauge of wire you run from the battery to the panel. On my Renegade I used a 30 amp fuse and 8 gauge wire. Fuses protect the wiring, not the stuff you are powering. Any electronics that requires fusing usually has it in the unit itself.

[Peter HK]

For interest here's a graph of depth of discharge vs cycles for a premium brand of AGM batteries (Lifeline).

As you can see the decay in cycles doesn't really have a sharp cutoff (though a logarithmic scale) and essentially the less the discharge the better.

The 50% figure of about 1000 cycles fits with regular workboat use and shelf life of the battery. 

Interestingly you can get 100s of cycles even with a very deep discharge so if you use it only infrequently you can get years (the lifespan) from the battery.

I have seen similar graphs for cheap batteries with some showing only a few cycles after deep discharges so a lot depends on the quality of the battery.

Cheers 

Peter HK

Edited December 1 by Peter HK
clarity

[Jonathan M. Cohn]

I left the boat and the batteries for 9 days. The weather was cool, occasionally below freezing, but not brutal cold. The batteries normally sit at 12.6 or 12.7 when full but off the charger. On returning to check the batteries, they were both reading 12.6. I plugged the battery charger into my power bank 110 port and its battery for 1.5 hours. They were both showing 14.4. This is normal right after charging but quickly drops to 12.6/12.7 after a short time. I will check again next week.

 

I don't know the proper terminology but I have three 12v, 92 amp batteries for a total of 3312 watt hours. Of course, only half or even 40% of that can be used without harming the battery. My goal is to never see them measure below about 12.3 with normal use. For this storage plan, I am hoping to never let them get below 12.5.

[Don Silsbe]

According to this chart, you can go much lower than 12.5 without worry.