[dtgriscom]

Question: if a LiIon battery can't deliver as much energy when cold, where does the lost energy go? Is it just unavailable, and becomes available again when warmed up? Is discharge less efficient, so the energy is wasted? Or does charging stop early when cold, so there's less to be discharged in the first place?

[stavros]

This is an educated guess, but I think it becomes less efficient, so it heats up, and then performs better as it heats. I assume this to be the case because I charge my RC plane LiPos the same way every time, and they take the same amount of energy, but flying in the winter gives much shorter flight times. Since the battery is warm after a flight, even in the cold, I don't think the energy is still there the battery is still discharged when I take it home), so it must just be much less efficient and wasting a lot of energy as heat.

I assume it's just that its internal resistance rises when it's cold, but I might be wrong.

[coryrc]

> Is discharge less efficient, so the energy is wasted?

Yes. It's mostly wasted as heat inside the battery. I think there's also a temperature relationship to open-circuit voltage? But the predominate effect is from elevated internal resistance.

[cogman10]

I believe you are correct. Temp causes the voltage to drop faster. It does raise as the battery heats up.

[pfilehats]

Easiest way to model this is from the cells impedance. Essentially think of the cold limiting ion motility in the electrolyte phase, and that resulting in a higher impedance, that works out as a voltage drop at the cells terminals, so the cell has a limited depth of discharge, vs at higher temperatures.

You can read about EIS here: https://www.gamry.com/application-notes/EIS/basics-of-electr...

[goalieca]

Batteries can freeze solid. It takes energy to keep them warm with an heater. Then there’s cabin heating which is usually warmed by heat from combustion in a gas engine.

[beAbU]

Internal resistance increases, so the battery heats up more when delivering an amount of energy. So some of the battery's stored energy goes to waste as heat.