regenerative braking in winter

I was out this morning in weather that might seem mild to many of you, but cold enough to affect my battery performance.

I know I should not [fast-]charge my battery when it's freezing cold. What about regenerative braking? Is that a light enough charge that it's harmless, or to put it another way does it maybe do more harm than good?

The details, it was near freezing, 32° to 40°F (or maybe 0 - 5°C if I had been in Vancouver BC.) The battery is nominal 12 Ah LiFePO4, regen stat according to the computer is usually around 12-14%, maybe over 300W at the beginning of brake down.

donn said:

I was out this morning in weather that might seem mild to many of you, but cold enough to affect my battery performance.

I know I should not [fast-]charge my battery when it's freezing cold. What about regenerative braking? Is that a light enough charge that it's harmless, or to put it another way does it maybe do more harm than good?

The details, it was near freezing, 32° to 40°F (or maybe 0 - 5°C if I had been in Vancouver BC.) The battery is nominal 12 Ah LiFePO4, regen stat according to the computer is usually around 12-14%, maybe over 300W at the beginning of brake down.

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If you store the battery inside it won't get cold under use. Otherwise you can turn off regen if it is cold.

I have been using regen braking every winter, down to -20. I use regen only in the winter, because slippery conditions are making it useful, and because I lower the power of my bike during the winter. In the summer, when my bike is set full power, regen does kick too hard and I prefer the brake.

My battery is high C rate RC lipo and the bike is parked in a heated garage. It doesn’t suffer from the cold, especially that my rides are short in cold weather.

Above freezing temp, spring or fall, I ride full power. I start setting a bike for the winter when the streets are dirty with snow and slush.

Some batteries are not suitable to operate in extreme cold. All batteries have lesser capacity in the cold, but low resistance RC lipo does pretty good.

It's probably fine, but to know for certain:

You have to measure things on your system to know what it's capabilities are, and match them to the spec sheets for the battery (or the cells in it), if you can find out what they are. If you built it, that's relatively easy; if it came prebuilt it requires some disassembly unless the seller/maker can tell you what's in it (assuming they can be trusted to actually know for sure--most have no idea).

Measure the temperature of the actual battery cells throughout the pack, while in use (when you'd be charging them via regen).

Find that temperature range on the spec sheet chart for the cells, taht shows what charging current they can take at what temperature.

Measure the regen charging current, both amount and time.

Compare taht with the chart.

If the current is within the range allowed by the charge at the temperature range the cells are at, then there's no problem.

If it exceeds that, then your best bet is to warm the pack up to the point it won't be a problem. There's many ways to do that--the simplest is just to keep it inside with you until you actually use it, and insulate it from the cold when you are riding so the heat doesn't escape.

Threads around the forum on winterizing, or insulating, or heating, etc. of battery packs have lots of info on it. Or you can just experiment.

The procedure is interesting and I appreciate the thought, but I'm not going to be carrying that out, so I guess I'll go with "probably fine", and maybe hedge my bets by using the front brake more (no regen) when the battery is extremely cold.

Or...keep the battery warm, and not have to worry about anything.

It's very easy to do.


Keep in mind that if you ride on slippery surfaces, the front brake is often unusable, because you lose all steering the instant that wheel skids. If you skid the rear you can usually recover from that, or at worst wipe out the rear. Lose the front and you don't have much of a choice in where you're going anymore, unless you're well-practiced at that sort of thing.


If you *have* to stop using regen, I'd recommend just unplugging the ebrake connector, if you don't ahve the option to just turn it off, rather than losing an entire wheel's braking. (assuming that your rear mechanical brake works, but that you can't use it without engaging regen too).