# Regenerative Braking with a Cold Battery



## Jemez (Jan 16, 2020)

I'm planning on ordering a LR AWD M3 in the next few weeks. Since I do a lot of driving on steep mountain roads, I'm a bit concerned about recent reports that software updates have reduced the amount of regenerative braking with a cold battery. 

One scenario is parking at a local ski area all day, 20F temps, with no option to plug in. The road out drops about 2,800 ft in the first 8 miles. Speed limit is 45 mph, with 25 mph in the steeper spots.

Is the regenerative braking going to be enough to keep to these speeds, or is the car going to have to rely on the mechanical brakes? In an ICE car I won't want to ride the brakes down this hill. I shift into a lower gear. Thoughts?


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## Bigriver (Jan 26, 2018)

Welcome to the forum.

I’m on my 3rd winter with Tesla and not noticed any recent decrease in regen. However, it is and always has been reduced with cold temperatures. I regularly take my model 3 to a ski resort, and have an initial 7 mile descent to the first stop sign. Not sure the elevation change for that stretch of the road. When I have no regen, I may have to tap the brakes once or twice, but it is not like having to ride the brakes in an ICE. Actually, the biggest thing I notice is that I’m not having to touch any pedal most of the way down. When I do the same road in warm weather and have full regen, I have to keep my foot on the accelerator the whole way. Having to hit the go pedal even when going downhill is quite an interesting adjustment!


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## Klaus-rf (Mar 6, 2019)

Regen probably will not be enough. 

And I wouldn't worry at all about using the fricti0n brakes. At those temps you will have e very hard time getting them up to temp.


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## Ed Woodrick (May 26, 2018)

Don't worry. Even if you need them, you will end up using them less than other cars


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## JWardell (May 9, 2016)

This year's software is MUCH better at heating the battery and increasing regen than last winter, and does so quicker as you drive. But if you preheat your car from your phone for 5-10 minutes, it will also heat the battery and you will have regen right away for your trip home. Really nothing to worry about.


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## Jemez (Jan 16, 2020)

Thanks for all the replies. Sounds like it won't be an issue at all.


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## FRC (Aug 4, 2018)

I just made a 3000" descent in 15 miles in 20F weather. Regen was limited, but I only used the brake on the 4-5 switchback curves. The rest of the way the available re-gen was ample. As others have said, you'll be on the accelerator where you used to be on the brake in an ICE car!


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## JeffC (Jul 4, 2018)

Several factors: when the battery is full, regenerative braking can't work because there's literally no place for the ions to go back into the battery electrode. (Regenerative braking charges the battery by converting kinetic energy to chemical. If the battery is full, it can't be charged further.) Therefore don't charge to full except in the very rare case of starting a very long trip.

Second, physics dictates that Lithium ion batteries have less capacity when cold, so if things are cold, the battery may also not be able to take regenerative braking power as effectively as when warm.

In practical terms it's not a big deal: don't charge to full. And the battery management system does a good job of keeping the pack warm. if regen isn't fully available for either reason, then use the brake pedal.


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