Best temperature for batteries (LiFePO4)

What is the best temperature for server rack type LiFePO4 batteries? I put mine with the AIO in a dedicated shed that is under a roof overhang on the northern side of the building, it's never in the sun. The AIO insists on indoor installation, so I went overboard with wall thickness etc..: wood framed, insulation, Tyvek on outside over OSB, fully sheetrocked inside.

I built this during rain season and keeping humidity low was a priority for me.

I did not expect that the AIO would generate so much heat. Humidity is under 30% when it rains!
Outside temperature is 7C at night and 17C at day time (today).

Temperature range in the shed


And that's after I added a ventilation in and out (4" pipe with inline blower, 100cfm)

Now the batteries. Their temperature ranges between 28 and 31C (as of today).


I am concerned that in summer these batteries will be closer to 40C!!

Should have made the shed bigger.

What temperature range do other people target?

I feel your pain. You may notice that the air in the shed is cooler near the floor so if possible place the batteries closer to the floor but above any potential water level. Batteries not only store electricity, they store heat. Heat, like the state of charge takes a while to change. If you have access to the tops of your cells (DIY) it’ll help to blow air over them as long as air is COOLER than the cells. The terminals and busses are excellent heat conductors and radiators to pull heat from the core of the cells. When your shed cools down cooler than the cells ( when your inverter isn’t heating it) is the best time to cool them down to get ahead of it. I have a fan to cool them on a timer. The rest of the time there is no air moving around the batteries (stagnant/still) because I don’t want the hot air heating them. It is a good idea to deflect away (barrier/partition) hot air from the inverter and draw the hot air out with a vent fan. Remember that you need to provide an intake for fresh air if your shed is well sealed. Every location is different so look temperature differences, times and airflow to your advantage.
Good luck.

5-40 c. Under 30c is better. Wouldn't want more than 50c.

Note: you can discharge at lower Temps, but you should not charge below 0c. Hence 5c just to be safe.

On a really hot day the air at head level gets to 45c but my batteries rarely get over 33c because of aforementioned management.

Weird, I did not get notifications about these responses. Thought just nobody was worried about temperature.

Skypower said:

notice that the air in the shed is cooler near the floor

Click to expand...

yes, I did notice that. Especially since my AIO blows warm air out at its bottom, which is like 4' below the ceiling. The batteries are in a stack. Lowest battery always coolest.

I have a fan at the bottom near the battery stack that blows the cool air at the floor upwards.

Skypower said:

Remember that you need to provide an intake for fresh air if your shed is well sealed.

Click to expand...

Certain times of the day the batteries show a higher temperature than the room temperature (measured near AIO). These would be the best times to cool the batteries.

Also, I expect everything to change as outside temperatures rise. Right now they are below 10C at night and 15 to 20C at day time. Easy to cool with a 4" inlet then.
Yes, I do have a 4" intake near the ceiling on one side and the 4" exit on the opposite side. The exhaust side has a inline fan attached to the ABS pipe that I embedded into the wall. ABS pipe on the inlet as well. I do have 1/4" mesh in front of the ABS, concerned about critters now.

Portable air con or window unit. Smaller space works to your advantage.

LiFePO4 batteries like the same temp you do. 25*C or around 75-78*F.

Anything higher or lower can speed up degredation, and anything lower will result in slightly less capacity as well.

I keep my garage at 78*F for this exact reason. Even when it's 115*F outside.

First I’ve heard of the 75 eff lower limit. Interesting.

See posts 9 and 12

Cooling them below 25°C will extend their service life by slowing parasitic reactions and electrolyte degradation at a cost of slightly less capacity. But you cannot let the electrolyte freeze.

Bluedog225 said:

Portable air con or window unit. Smaller space works to your advantage.

Click to expand...

Just a follow up on this. The weather forecast had announced some hot days and I happened to find a window AC unit (Hisense) in my storage that I had obtained for free over a year ago.. so this was installed last Friday.

I was no longer able to maintain the temperature target with fans alone.

I had never owned or operated a windows AC, one reason being that our house has ceiling fans everywhere, they are ugly, and perceived as expensive to operate compared to a fan.

Well, I can report that the windows AC set to 77F in Eco mode uses most of the time just 100W during cooling although I observed 600W a few times. In standby, it's just 1W (!).

Over 24h it has used between 1kWh and 1.5kWh depending on heat produced by the AIO.

It actually makes sense.

The AIO burns 90W idle consumption = 2.xkWh a day, which heats up the shed. It should not take more to cool it.

Interesting detail: the 2 fans sucked 80W combined.. but on a hot day, nearly 24h straight which was about the same as the AC unit.

Very happy with the outcome.

Batteries' cells all show the same temperature 25.0C to 26.5C

CaliSunHarvester said:

Just a follow up on this. The weather forecast had announced some hot days and I happened to find a window AC unit (Hisense) in my storage that I had obtained for free over a year ago.. so this was installed last Friday.

I was no longer able to maintain the temperature target with fans alone.

I had never owned or operated a windows AC, one reason being that our house has ceiling fans everywhere, they are ugly, and perceived as expensive to operate compared to a fan.

Well, I can report that the windows AC set to 77F in Eco mode uses most of the time just 100W during cooling although I observed 600W a few times. In standby, it's just 1W (!).

Over 24h it has used between 1kWh and 1.5kWh depending on heat produced by the AIO.

It actually makes sense.

The AIO burns 90W idle consumption = 2.xkWh a day, which heats up the shed. It should not take more to cool it.

Interesting detail: the 2 fans sucked 80W combined.. but on a hot day, nearly 24h straight which was about the same as the AC unit.

Very happy with the outcome.

Batteries' cells all show the same temperature 25.0C to 26.5C

Click to expand...

That's cool to hear AC was almost the same usage as the fans, but you maintained a much lower temp!

This concern is why i insulated my garage this year with spray foam, and put a Mr Cool in there. It is doing a really good job of keeping the garage in at a nice medium temp. I am going to add a vent up high as well, just to exhaust the hot air.