Hi All, I think you folks are pretty knowledgeable and might be able to give me some places to look that I haven't thought of. This is for an oddball industrial use at a remote site without power. Need a battery solution that will be able to keep a small video camera powered (think like a trail-cam), for up to 2 months, in very cold condition (say -25c, -15F). I don't have the power draw in front of me, but it's probably a few hundred miliamps. This location is very far north where cloud cover, and low-angle of the sun in winter mean the solar panels are nearly useless for December and January. Have previously used things like 2x Gel-cell deep cycle batteries, but they haven't been reliable if the temps drop or the sun stays away a little longer than normal. Can always add more and more batteries, but at some point, there has to be a better solution.

How are the alternative battery chemistries for extreme cold? Are there things I should be looking at?

Thanks for the assistance, and if the Mods think there's a better sub-forum, feel free to move it.

 

LiFePO4 is OK to discharge under 32°F. But you shouldn't charge it below 32°F. If you have a warming system for the LiFePO4 battery that keeps the battery above 32°F then that would work. The warming system on my LiFePO4 doesn't take much power, but I do have it well insulated and the solar panels replenish what the warming system draws.

A lead acid battery that is discharged will freeze and that's bad.

 

Cold is the enemy of batteries. I've had great luck with AGMs up to -42F without being plugged in. My OBS will start after sitting for a month and it being -20F. Problem with AGMs is that as they discharge the electrolyte turns into water so a nearly dead AGM will freeze easily. I've used AGMs in negative double digit temps for weeks at a time but never longer and not deep cycle like you are looking to do. You would have to have a way to recharge them because the longer they stay discharged the more damaged they can become.

 

Thinking outside the box a bit:

could a small wind generator be used in this location to maintain the battery?
If there is enough wind, and the generator is functional at the expected temperatures, then a simple AGM or FLA could be used.

 

I have zero knowledge of wind generators. There is a subforum on the DIYSolarForum for those if you're interested.

https://diysolarforum.com/forums/diy...roelectric.46/

 

I have Renogy LiFePO4 batteries that include a heater, and automatically prevent charging until the temp is above 5C - could be an option, although in extreme cold it might never get that warm (maybe if you insulate it a lot). But if your draw is low enough that might still suffice.

 

The internal heater in those LiFePO4 batteries is interesting. I've been doing some reading and it doesn't draw any power from the battery itself, just from the solar panel when it's functioning. So in theory reduces the effectiveness of the solar panel, but should allow the batteries to charge.

There are a variety of insulated battery boxes around that would help with this too. So the internal heaters shouldn't have to work too hard.

Still not convinced this will be the solution, but something to research anyway.

 

The BMS will run the internal warmer when it sees a charge current. Until the battery temperature is above the low temperature charge cutoff, the battery receives no charge. A battery that is at 0°F will take a long time to reach that threshold. It could be a couple of hours, which means the battery will miss out on valuable charging time. It depends on how aggressive the warming plates are and how much power the solar panel produces.

I'm not a fan of the internal warmers, but they're better than nothing.

 

It sounds like there are a few factors to consider:

- How much energy will the small video camera use?
- What minimum temperature will the chosen battery need to maintain for reliability/safety/longevity/etc.?
- How much power will be required to maintain that temperature?
- How much mathematical margin do you want to add to the equation?
- How many of this battery do you need for the above math to work?

While I'm here, I suggest insulating these batteries a lot, unless solar etc. charging will create a lot of heat in them. Also, it would probably be a good idea to put them on a thick layer of something that insulated from the cold, not straight onto concrete or bare ground etc. that can conduct cold to the battery.

Thinking a little further outside the box: If the battery of choice needs ventilation, and has a built-in vent, this would be better than having the battery enclosure filled with an ample supply of fresh air. That fresh air will bring the cold in with it, but if they self-collect and vent through a little tube, this can be greatly minimized and improve the math above. For those not familiar, I've seen this in cars where the battery is enclosed somewhere attached to the passenger compartment. They have a little vent tube that needs to be attached. An example would be the H6 group battery that lives under the second-row passenger-side passenger's feet in a Chevy Traverse.