Battery warming for Lifepo4 batteries.

[dbhost]

What are folks doing to keep their lifepo4 batteries above freezing when the weather is well below freezing?

I see battery heater pads. I was wondering if any of them are actually effective and have low power draw. Or maybe something different? I'd like to be able to use my Lifepo4 battery below freezing without destroying it.

 

[DiploStrat]

Mine are inside the camper - no heater.

But remember, you only need to keep above freezing when charging. They can discharge at any temperature. The power draw for the heater usually only comes from the charging source.

You do need to warm the batteries when coming out of storage, etc., but overall, this is not quite as much of an issue as people fear.

 

[Buddha.]

I worked on a Ram van that was a class B conversion last week. The batteries were mounted underneath the van in no kind of enclosure. No heating pads, and they were dead. Worst design.
I would think having them in the living space would be fine, as long as they’re not tucked up against an uninsulated wall behind a cabinet etc.
They just need to be above freezing. Even the most diehard winter campers would keep their living space warmer than that.

 

[dbhost]

So my camper, at this point is a hi top shell with a platform bed, and an electrical compartment. Since I am using Lifepo4 batteries with no concerns RE: offgassing into the living space, the electrical compartment is within the living space / truck bed. Insulation, such that it is is only a bedrug. I am more concerned about getting these batteries above, and keeping above freezing before I head on down the road with the DC to DC charger. The chances of me hitting sub freezing temps while in transit are possible but VERY low (Texas after all). However does everyone remember the big freeze in 2021?

I was originally going to mount battery under the bed of the truck but I was also originally planning on an AGM battery. After comparing capacity, usability, and cost, I went lifepo4. However it does consume interior space, something I am not loaded with...

 

[DiploStrat]

From what you described, you are planning an unheated space and not talking a very big bank. Stick them in a box, plywood would do, and buy heated batteries, or stick a tank heater underneath. Use an automatic or manual switch to control the heaters and only run them just before or when charging.

N.B. Many good lithium batteries have temperature sensing BMS's, so the batteries should protect themselves if you are the least bit careful.

 

[dbhost]

My batteries are already in hand, bought in Texas not considering freezing temps so no heated battery for me! Ooops... And yes, well. Heated when I am in the space. It would be incredibly stupid to leave a buddy heater for example, running in the back of the truck going down the road to keep the batteries warm. But when I am in the camper, or even just banging around for the day but not driving, so not DC to DC charging, keeping a heater going is no big deal...

My concern really is more of a heading up into the mountains to camp thing. Don't want the batteries getting too cold as I go down the road. There are some solutions though, at least in theory. Starting off with get the camper good and hot, make up some hot water bottles and keep them around the electrical cabinet (yeah, water and electricity there's a great idea!) and keep em warm that way.

Chemical heat packs maybe?

I am talking about rare use in a pinch sort of stuff, at least for now. Down the road, maybe a different arrangement.

 

[WanderingBison]

A couple of things for your to consider -

As @DiploStrat already mentioned, MOST quality LiPo batteries have an internal BMS that will protecting them from charging when below their “safe” temperature (around or a little above freezing) but will still allow you to discharge, to allow for continued use but could also power a very small heating pad to help maintain the battery above the required temperature.

A battery is a really large, dense mass so if its well above the “safe” temp, it will usually stay above that temperature for some time, especially if you are continuing charging and discharging the battery. Simply running current in or out of the battery will raise it’s internal temp.

In my experience, the biggest issue is that in cold temperatures, if I continue using the batteries even if I’m not in the truck and heating the space (think fridge, lighting, etc.) and therefore discharging the batteries, but unable to charge because I may have gone below the “safe” temp.

I’ve only gotten myself in “trouble” when I was away for a couple of nights and the battery weren’t being charged at all either because I didn’t have DC-to-DC going or solar charge, while the habitat temperature kept dropping.

The worst that ended up happening was that the battery stopped charging because of the temperature and fully discharged (well, until the BMS shut it down).

Little or no harm, except that it was a pain to get the battery back above the “safe” temp and charging, since now my whole system had disabled charging. After it happened a second time, I’ve been EXTRA careful and carry a Noco Genius charger that allows me to partially charge the battery before connecting it back to the truck’s system.

Hope this helps.


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[JaSAn]

You didn't specify what kind of trips:

3 day weekend where temps might get to low 20s,​

14 day hunting trip where temps might not get above freezing?​

Different solutions.

Truckers use a 'battery thermal wrap' to warm up starter batteries. The one I have used was 120V; there might be 12V versions.

For short trips:

Preheat batteries at home, store in insulated battery box. Should keep batteries warm for a long weekend in mild below freezing temps.​

For long trips and/or constant cold temps:

You will need enough energy to heat batteries (or keep batteries warm). Generator, truck alternator, solar; you need to account for the added energy you will need to heat your batteries.​

 

[Alloy]

Make sure to have some air gaps between the battery and the heating pad



Some BMS have 1 temperature sensor that is ********......one on the top of the battery (that's sitting on a freezing floor) next to the undersized cable or BMS that throws heat off during charge/discharge.

A good BMS has more than one temperature sensor. Top and bottom of the bank

To make doubly sure nothing goes wrong when out in the cold I'd be using a Bluetooth thermometer that has an alarm. Like Sensor Push or Inbird.

 

[OldGreyShoe]

If you're looking for a quick DIY, I did this and has worked for me: I have a GoalZero 1400, and built a Reflectix box that fits over the top. When I'm at sub-freezing temps I'll open up a few hand warmer packs, give them a shake, and then put them on the sides, top, etc of the battery, and put the Reflectix cover over it. Has worked overnight down into the mid teens and is a super inexpensive approach.

 

[Adam_Cole]

I wrapped my Lifepo4 cells in an RV tank heater and wired it to temperature controller. Kicks on at 34 degrees and turns off at 40.
I have an Overkill Solar BMS with Bluetooth so I can monitor cell temps and turn on and off charge and discharge just in case.


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