preheating lithium battery for less voltage sag - maximum temperature

The colder days have arrived here and I've started preheating my pack before riding. I usually try and heat the pack to around 30 Celsius. My understanding is that a higher starting temperature will reduce the internal resistance of the cells. This seems to work well as it keeps my max power and speed available.

My question is what would the maximum approximate temperature be for heating my battery pack before it has a negative effect on cycle life etc?

This graph illustrates what I'm experiencing, but what are the downsides of pre-heating a pack?


Thanks!

40-45degC for racing is generally about ideal. Leaves you with a little headroom to climb from discharge heating.

I have read that "White Zombie" and the KillaCycle both warmed their pack to get the max performance that was possible from their battery packs. I'll bet LFP's post above has the accurate numbers...good info!

edit:

30C = 86F

40C = 105F

A long time ago, i started a thread showing that lithium batteries' internal resistance quadruples when you go from room temperature to freezing.

Therefore if you have a battery with TONS of headroom in the maximum discharge rating VS what you actually pull, you can forget having to heat your battery at all
( IE you're driving a geared motor on lipo packs or a big samsung 25R pack )

I think some heating would help and not damage the battery though, if you aren't in a position to go out there and pick up a new battery per my recommendation.

Thanks for the input folks, much appreciated! 8)

I am running my pack at the max discharge rating so no headroom here. It is definitely something to consider for a future pack but the problem is my power addiction takes over and I would probably max that one out too!

For the record my ride is only about 3.5km over 10-12 minutes:

This morning I was able to heat the pack up to around 31C and performance was good. Outside temperature was 9C.

This afternoon I was able to get it to 37C and performance seemed even better. At the end of my ride the pack was at 39.5C with an outside temperature of 15C.

I am going to shoot for 40-45C as per LFP.