Keeping a Battery Warm???

[Inq720]

I've skimmed through this thread, but its mainly about actually keeping the battery warm. I'm more interested in the why? And specifically... I'm wondering about storage. I'm on another boat forum and I share some of what I learn from this forum with them. Someone over there posted the excerpt below from a manual. I understand the battery needs to be kept above 32F for charging and 0F for use.

1. If I'm storing it over the winter and have diligently drained it to 50% SOC by one estimate or to 13.15 volts (< 40% SOC) by another reference, can I not leave it out in the cold?
2. Do I really need to keep it at 59F?
3. Is this some company being overly conservative?
4. Or could this be a company supplying an excuse to void a warranty if someone didn't keep their batteries warm?
5. If, it is a valid concern, what is the basis (mechanism) for this?
6. Are we talking about cutting the life in half, or 1%?

Thank you for all your all's help.

 

[HRTKD]

Hard to say. Maybe they are being conservative. Is that for a Lithium-ion battery or LiFePO4? Most of the battery warmer discussions on the forum are for LiFePO4.

 

[Inq720]

I have the Lishen cells, but someone on the other forum asked me about it. They're predominantly AGM battery guys. They just love to hear special things like you have to keep your batteries warm at 59F. Especially, since they contacted the company and the response was the typical marketing tier-1 tech support (reading script/no substance). And recommended they just bring them into the house during the winter. The AGM guy's tend to go non-linear all over that kind of BS!

It appears that Xantrex is a LiFePO4 company.

 

[jwelter99]

I've skimmed through this thread, but its mainly about actually keeping the battery warm. I'm more interested in the why? And specifically... I'm wondering about storage. I'm on another boat forum and I share some of what I learn from this forum with them. Someone over there posted the excerpt below from a manual. I understand the battery needs to be kept above 32F for charging and 0F for use.

1. If I'm storing it over the winter and have diligently drained it to 50% SOC by one estimate or to 13.15 volts (< 40% SOC) by another reference, can I not leave it out in the cold?
2. Do I really need to keep it at 59F?
3. Is this some company being overly conservative?
4. Or could this be a company supplying an excuse to void a warranty if someone didn't keep their batteries warm?
5. If, it is a valid concern, what is the basis (mechanism) for this?
6. Are we talking about cutting the life in half, or 1%?

Thank you for all your all's help.

View attachment 38264

Do you live somewhere where winter is 3+ months constantly below 15C? For most of us the freezing periods are short - maybe a few days to weeks - with warmer periods in between. This means it maybe not >3 months but a couple 1 week periods below 15C.

 

[Inq720]

As I mentioned, this is for my curiosity AND for another forum. Of which there are many on that forum who live in New York, Michigan, Wisconsin, Colorado, Canada, Norway, Sweden, etc. So... yes, there is "someone" who lives in below 0C for months. Either way, I'm looking for the why's. White papers, theories, why 15C. Before this line in a company manual, I was comfortable with dealing with 0C occasionally myself. Convincing many people they need to store batteries at 15C when they're used to car batteries... is a non-starter.

 

[Luthj]

LFP do not need to be heated during storage. Lithium electrolytes won't freeze until -22F/-30C, so I wouldn't let them get colder than that. If the area experiences cold snaps overnight below -30C, LFP would be fine inside a building, as that would cushion the high/low temps.

LFP do need to be kept above freezing to charge. It depends on the cell specifics, but charging above 0.4C is best done at temps above 65F.

Discharging is safe even at -22F/-30C. However performance will drop off quite a bit under 32F/0C. Lead acid also suffers from significant performance reduction in cold weather. Lead acid batteries will freeze if discharged to 50% at temps below 0F, so they aren't immune to this either.

Keeping an LFP pack warm in cold weather is not difficult. I have a 7kw pack arranged as a cube underneath my all season overland van. It is insulated with 1/2" XPS foam on all sides. I have a 65W heating pad on a thermostat to keep it above 33F. Even in sub zero weather the pad doesn't run at 100%. If I am charging/discharging at high rates I don't need the pad at all in 10-30F weather.


There are some drop-in LFP batteries which integral heaters. When a charging source is applied, they shunt the power to heating film inside the battery. Once the cells are warm enough the charging power it sent to the cells. These batteries can be operated without special considerations in all but arctic weather. Though in extreme cold using an insulation blanket/covering will improve charge efficiency.

 

[jwelter99]

As I mentioned, this is for my curiosity AND for another forum. Of which there are many on that forum who live in New York, Michigan, Wisconsin, Colorado, Canada, Norway, Sweden, etc. So... yes, there is "someone" who lives in below 0C for months. Either way, I'm looking for the why's. White papers, theories, why 15C. Before this line in a company manual, I was comfortable with dealing with 0C occasionally myself. Convincing many people they need to store batteries at 15C when they're used to car batteries... is a non-starter.

Sorry missed that. I think the answer to this is reduction of warranty issues.

As Luthj points out storage is safe quite a bit lower, as is discharge.

Think about a EV vehicle parked outside - they function fine albeit with reduced range.

I grew up in the Yukon where -45C was the temp where school was cancelled and -30's for weeks was not uncommon. So I know these areas exist, but also now question why humans choose to live in them year round.

 

[Inq720]

Sorry missed that. I think the answer to this is reduction of warranty issues.

As Luthj points out storage is safe quite a bit lower, as is discharge.

Think about a EV vehicle parked outside - they function fine albeit with reduced range.

I grew up in the Yukon where -45C was the temp where school was cancelled and -30's for weeks was not uncommon. So I know these areas exist, but also now question why humans choose to live in them year round.

You're a tougher man than I. Used to be a snow skier. Now, I don't go outside for pleasure below about 40F. Sailing... it has to be in the 70'sF.
I was leaning toward, the company trying to have an exit strategy for warranties. I also thought of EV's parked outside, but I just assume they have heaters for the cells. I'm sure Tesla does.

LFP do not need to be heated during storage. Lithium electrolytes won't freeze until -22F/-30C, so I wouldn't let them get colder than that. If the area experiences cold snaps overnight below -30C, LFP would be fine inside a building, as that would cushion the high/low temps.

LFP do need to be kept above freezing to charge. It depends on the cell specifics, but charging above 0.4C is best done at temps above 65F.

Discharging is safe even at -22F/-30C. However performance will drop off quite a bit under 32F/0C. Lead acid also suffers from significant performance reduction in cold weather. Lead acid batteries will freeze if discharged to 50% at temps below 0F, so they aren't immune to this either.

Keeping an LFP pack warm in cold weather is not difficult. I have a 7kw pack arranged as a cube underneath my all season overland van. It is insulated with 1/2" XPS foam on all sides. I have a 65W heating pad on a thermostat to keep it above 33F. Even in sub zero weather the pad doesn't run at 100%. If I am charging/discharging at high rates I don't need the pad at all in 10-30F weather.


There are some drop-in LFP batteries which integral heaters. When a charging source is applied, they shunt the power to heating film inside the battery. Once the cells are warm enough the charging power it sent to the cells. These batteries can be operated without special considerations in all but arctic weather. Though in extreme cold using an insulation blanket/covering will improve charge efficiency.

This all seems consistent with what I've learned so far. And I know at low temperatures there is some reduction of capacity for that cycle, but have never heard if there is any long-term effects once the temperatures rise again.

 

[Luthj]

And I know at low temperatures there is some reduction of capacity for that cycle, but have never heard if there is any long-term effects once the temperatures rise again.

To clarify, there isn't any permanent capacity reduction from discharging or storing at low temps. All chemical batteries have reduced performance when cold, that's just a matter of energy extraction being less efficient at low temps.

In fact storing lithium at low temps reduces calendar aging. For example at 75F the capacity loss per year is X, and at 50F the capacity loss is about X/2.

 

[Inq720]

To clarify, there isn't any permanent capacity reduction from discharging or storing at low temps. All chemical batteries have reduced performance when cold, that's just a matter of energy extraction being less efficient at low temps.

In fact storing lithium at low temps reduces calendar aging. For example at 75F the capacity loss per year is X, and at 50F the capacity loss is about X/2.

Thank you. This is consistent with what I "thought" goes on. That one is "storing" versus adding cycles... just make common sense that long term life would get better. Still it bothers me that a company would state you need to bring your batteries inside in 59F.

 

[Luthj]

About half the companies making LFP drop ins don't know jack S**T about LFP cells. Heck early on LFP cell makers were specifying a 4.2Vpc charge termination points. Most users and even some corp engineers who were familiar with lead, just let the cells sit at that voltage for minutes or hours. The MFGs literally meant terminate the second the charge hits 4.2Vpc, and don't float. Now we know much better of course.

Long term storage of LFP batteries should be under 90% SOC for certain, and ideally below 70%. For drop-in styles where you can't disconnect the BMS, store above 20% SOC. The lower the temperature the better in general, though I would stick with 30-40F if you have a choice. High temps and SOC accelerate the natural degradation/capacity loss.

Lead acid also suffers from high voltage and high temp degradation. It just so happens that sulfation from partial SOC storage produces more capacity loss than high SOC storage. As with LFP low temperatures decrease self discharge and reduce capacity loss due to aging.

Remember, these aging effects are independent of cycles. Cycle capacity loss for LFP will stack with capacity loss based on aging. Aging is a factory of average SOC and temperatures. Voltages above 3.4Vpc for extended periods will accelerate the aging process, hence why LFP float voltages are <3.4V. I like 3.35V myself. Same goes for high temps. Calendar aging/loss is typically around 0.75-4% per year. 4% would be storing a cell at 90F+ average temps, with constant float charging 3.4V+.

For lead each 15-20F rise in temperature will cut a the batteries calendar life in half.

 

[Bossrox]

I'm confused by your 1st post as why you would drain a batt before storing it? A batt that will be unused for a long period should be fully charged before so. Storing a partially charged battery will cause sulfation but the storage temp won't have any effect on it being dormant, but in use, doesn't have good load capacity in freezing to below that. If you are using a lead acid on an active system where it's in an unheated structure, you would be better served to slide a plant heating pad under your batts & wrapping them in insulation. The ideal working temp for lead acid is 77 degrees. All my batts are in a well insulated cabinet on heating pads that keep them @ 70 degrees during the winter & a duct piped into the cabinet from my A/C'd shed to keep them from getting too hot.

 

[Inq720]

I probably should have re-iterated in my question for clarity, but his question pertains to Lithium based batteries, not lead-acid. Lithium batteries should not be stored fully charged.