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Battery maintenance

Mon Jun 22, 2020 5:51 am

I cannot find information about how best to look after the battery. Is it best to run it down and then charge - or keep it topped up from a sensible base.
This is important during the COVID-19 lock down when I am not using the car much. i bought the new 120Ah on the 1st march and have just done 600 miles.


George Martin

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Location: Dallas

Re: Battery maintenance

Mon Jun 22, 2020 8:25 am

According to the manual, any extended time of non-use, BMW recommends the car be at full charge, and plugged in to a charger if possible. The mantra on the BMW i3 FaceBook page is "ABC" (always be charging).
Mark H.
2015 i3 Rex, Capparis White, Tera World, Technology & Driving Assistant, Parking Assistant, Harman Kardon Audio System, 19 inch 427 wheels, EVoInnovate EVSE

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Location: Nashua, NH USA

Re: Battery maintenance

Mon Jun 22, 2020 9:22 am

According to the BMW i3 book that's been around for awhile, a single charge from 0-100% puts the same wear on the battery as ten charges of 90-100%. Personally, I just plug mine in when I get home, and leave it. In the six years, my battery range is slightly lower, but not much. If the car is plugged in, you can leave with a full battery if you decide to precondition it. While you can condition the cabin without being plugged in, in the winter, you will also find it useful to precondition the battery pack, and that requires it to be plugged in. That battery warming process can take up to 3+ hours. You'll use more percentage of your charge when the batteries are not conditioned, so in theory, you'd be putting more wear on them by not preconditioning them by setting a departure time. Using round numbers, say you can go 100-miles when they're conditioned and you go 20-miles. That's a 20% usage. But, if you do not precondition them, the car might go 80-miles in the cold, and you go that same 20-miles...that's now 25% of your capacity putting that much more wear on them.

The battery management in the car will not use the real full capacity on either end, so the batteries are never really fully charged or discharged before the readout shows 100 or 0%.

Unlike a simple phone charger, the power gets shutoff by the car when it thinks it is full.
Jim DeBruycker
2014 i3 BEV, 2021 X5 45e
(The i3 will be sold soon, <17K-miles, interested?)

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Re: Battery maintenance

Fri Jun 26, 2020 8:50 am

The closer you can keep the battery at 50% when not in use, the better it is for it in the long run, it's the way Li-ion batteries are.

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Re: Battery maintenance

Mon Jun 29, 2020 3:00 pm

I fully accept the OP mentions his car is a 120a.
Ours is a 94a REX and during the lockdown, the message popped up that the REX could not/did not do its maintenance cycle and an amber warning popped up. We couldn't go out and about and the car's charge was at 95%, so I ended up taking it out for a quick run with everything switched on to get the charge down to below 75% and be able to then tell the REX to keep the charge at the level. Had I been stopped by plod during this run, I'd got my story that it was an essential journey for me to remove the message on the display and reduce the risk of an expensive repair. LOL. So a full charge didn't help matters. Following that, we always tried to leave it at a charge level so we could turn the REX on. Now we can drive around without fear of being pulled over, its not as critical!
I think changing the REX is more expensive than changing the battery pack!

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