Value of Heated Batteries

[bajajoaquin]

This is not really a lithium DIY question, but I’m looking at putting together a heater and thermocouple for a lithium battery so it’s kinda DIY.

Anyway, I’m looking at the SOK 100ah battery for a friend who wants to cold weather boondock camp. My understanding of the SOK is that it draws the current for heating from the power source (solar, in this case) rather than from the battery. The theory is that it means it won’t try to charge until it’s heated itself up enough to work. However, on a system where it’s not plugged in all night, it seems to me that the battery temp could drop below the cold weather discharge threshold and then there could be no power at all.

If this is the case, a heated battery wouldn’t provide the over night operation that is required. I’d still be having to put a low wattage heating pad and thermocouple in the compartment anyway, right? That seems to indicate that I shouldn’t bother with a heated battery.

Thoughts?

 

[Rednecktek]

The low temp discharge setting and the low temp charge settings are radically different. The battery will often times still put out power down to -20c, but won't allow a charge until it gets back above freezing.

If your buddy is out cold weather boondocking and the battery compartment is getting below -20c, they've got bigger problems!

 

[bajajoaquin]

I guess I thought that the charge and discharge temps were the same. Thanks.

That got me to look at the SOK site and they say both charging and discharging to -4F. Seems like there’s not a lot of value even to the heated battery either. As you suggested, he’s not interested in camping in weather that cold.

 

[Rocketman]

When I built my diy MotorHome battery - I included a pad heater.

(At least a couple of years ago), You don’t want to charge a lithium battery below 32F. That can destroy the cells. Since we full-time and often it will dip to the high 20’s at night, I didn’t want to chance or worry about the battery.

My system will keep the battery in the low 40’s - that’s plenty safe. If we don’t get great sun that day - we run the generator.

 

[bajajoaquin]

When I built my diy MotorHome battery - I included a pad heater.

(At least a couple of years ago), You don’t want to charge a lithium battery below 32F. That can destroy the cells. Since we full-time and often it will dip to the high 20’s at night, I didn’t want to chance or worry about the battery.

My system will keep the battery in the low 40’s - that’s plenty safe. If we don’t get great sun that day - we run the generator.

Yes, I get that. A heated battery in that case will keep from charging a too-cold battery because the heat is provided by the charge current. But my worry is if you’re camping and it’s well below freezing that the low temp cutoff would trigger on the discharge side. And that doesn’t seem to be an issue at reasonable temperatures.

I think I’ll put in a low wattage heating pad and thermocouple anyway to protect him if he makes a mistake and gets caught out, but it doesn’t seem like a big priority.

 

[Rednecktek]

That got me to look at the SOK site and they say both charging and discharging to -4F. Seems like there’s not a lot of value even to the heated battery either. As you suggested, he’s not interested in camping in weather that cold.

That seems like a real failing on SOK's part as all my DIY's and pre-builts all say -20c for discharge. If SOK is kicking that up to -4c for discharge, that tells me Anything Other Than SOK.

 

[yodamota]

That seems like a real failing on SOK's part as all my DIY's and pre-builts all say -20c for discharge. If SOK is kicking that up to -4c for discharge, that tells me Anything Other Than SOK.

sok batterys are saying -20C, not -4C

 

[Tomthumb62]

But my worry is if you’re camping and it’s well below freezing that the low temp cutoff would trigger on the discharge side.

The low temp cutoff is for charging. If there’s one for discharging, it would be below 0F.

Anytime someone talks about needing to heat a battery, it’s so they can start charging again.

Unless you’re in Arctic conditions, you’ll likely never need to worry about discharging issues.

Keep the battery in a cooler or other insulation and if the battery is regularly being cycled (always under load), then the heat generated from discharging combined with external insulation may be enough that you don’t need any heating pads.