How does ambient Temperature affect LiFePO4?

Just what the title says, I'm curious how temperature affects the characteristics of a LiFePO4 battery. I have a 4S ("12v") battery that I will be using outdoors in a variety of temperatures ranging from 30F to 70F. Does lower temperature affect the capacity etc?

Not so much capacity, but being cold makes the chemistry reluctant to give up it's stored energy. So you charge at room temperature, to full capacity and then take it out in the cold. It'll sag more under load as it cools down, and so at the same load, it will hit LVC sooner. If you then return it to room temperature (without recharging), it will "give up" the rest of the stored energy.

This effect starts to be noticeable on my ebike pack at about 5 degrees above freezing, by about 15 below it's quite apparent but the pack still functions. I bring the battery inside with me where ever possible at these temperatures. At 30F I wouldn't expect much effect, unless you're pulling especially hard on the pack.

Mine is a 20Ah pack (48V) pulling 25A. Capable of much more though, 100A+ so that might have something to do with why it's not super apparent to me.

I noticed performance impacts from about 15*C. Even the difference between riding to work first thing in the morning at 14*C, and riding home after at 17*C was quite noticeable.

Probably wasn't very significant until about 10*C though.

All this said, my packs were about 6 years old, and done a lot of cycles, the effect would not be as severe from new.

Alright, thanks for the info. My battery is 12v 80AH and I'll be pulling 5-6A/hr. Generally speaking the temp will be 50-70F, but there may be rare times when I'll use it in colder conditions and I wanted to know how that would affect the battery. Sounds like it won't affect it too much for my purposes.

Warmer = higher operating voltage = more power.

I see about 60 km range on my scooter in winter (10-20'C) versus a comfortable 65 km in summer (20-38'C)

dustNbone said:

...being cold makes the chemistry reluctant to give up it's stored energy. So you charge at room temperature, to full capacity and then take it out in the cold. It'll sag more under load ... and so at the same load, it will hit LVC sooner.

Click to expand...

Here's an example plot for a commercial 12V battery at various temperatures. The test discharge rate is characteristically low, but the plots are indicative of the change in internal resistance. As mentioned, this causes the battery to develop a higher voltage drop for the same current draw and so hits LVC at a lower current.

Notice that the plot is for percentage of 'rated capacity' not 'capacity' which explains how some curves end at over 100% (!) -- but with a little stretch of the x-axis, a simple 'capacity' interpretation works okay and paints a slightly improved picture.

Notice also that the lower 10V cutoff for the test is at only 2.5V/cell. At a more conservative 2.8V/cell or more, the picture looks a bit less optimistic.

i got a bunch lifepo4's here. most of them take a dive when it gets under 10c. they tend to like higher temperatures.
regular lipo's usually behave more even until you pass freezing then the lipo craps out and the lifepo4 takes the lead again.

if people use their EV's as a daily driver i usually recommend putting heating in the battery that keeps the temperature at 20C at all times.
that way you never lose precious amps.

Fwiw, just putting insulation around a battery that is going to be discharged in freezing weather helps a lot. At least then the waste heat from discharging it doesn't go to waste.

But for sure, starting out at room temp best. if convenient to do so.