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Discussion Starter · #1 ·
Out-of-interest, how are people keeping their i3 12 volt battery in a good state of health during these prolonged lockdowns?
 

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2020 BMW i3S 120Ah BEV
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Personally I'm using it fairly regularly, so it gets a good charge at least every couple of weeks as well as regular enough, even if short, journeys.
 

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BMW i3 REx 2014
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In theory, just keeping it plugged in might be enough - the recovery method when the 12V battery is discharged was described in the now removed on-line BMW workshop manual as:
  1. open car door with manual key,
  2. open charge door with manual pull
  3. plug car in
  4. wait for 12V battery to 'fill' enough for relays to bring online the traction battery which then keeps 12V charging.
Not tested by me though.
 

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BMW recommend keeping the car plugged in if leaving for more than a few weeks. Not sure if this is best for long term battery life but you can keep the 12 volt battery topped up by an occasional run (every two weeks?) or by periodically plugging in. I haven’t heard on any forums reports of the 12 volt battery going flat but it is common on certain other models, particularly hybrids.
 

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I have seen zero evidence that by simply plugging the car in it makes any effort to charge the 12v battery.. if the relay is open on your charge outlet it can't charge the 12v from it, and the relay is open unless the HV is charging or the car is preconditioning.
 

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I wish Electrified app could display 12v aux battery voltage and SOC.
Well, at least it shows parameters of the HV battery: temperature, capacity Ah, SOC and SOH...
 

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Discussion Starter · #8 ·
Thanks all. I only asked because I have seen the ‘turning off non essential DC message’. The jury is out as to whether leaving an i3 plugged in will maintain 12 volt battery charge. It was suggested to me that the best way to maintain 12 volt battery health is to turn the i3 on a couple of times a week. This will engage the DC to DC 12 volt converter which runs for about 30 minutes after the car is locked. A few people suggested that simply unlocking and locking the doors would also turn on the DC to DC converter.

I agree that the BMW has built in a failsafe in that simple plugging in an i3 with a discharged battery will, after 30 minutes or do, start a 12 volt battery charge. I am trying to avoid getting into that state.
 

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BMW i3 REx 2014
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Three things to consider:
  1. flashing the lights via the app engages some relays, so this may charge the 12V battery - too cold to wait to hear the relays switch off
  2. the car will tell you if the battery is failing and so prone to premature discharge
  3. I think rusty brake disks are the main problem, so a weekly drive is a must - a few miles can be enough - kill 2 birds, etc.
 

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During the first lockdown our i3 (94rex) was plugged in with the granny charger for three and a half months without being used, the first time we used it after lockdown was as if we had been using it regularly, no issues at all.

ps, we live 75 yards from the Atlantic and the discs were rusty of course but after the first run (to run the maintenance schedule the Rex demanded) they were shiney and clean again, both back and front.....I felt the reverse just to check in case a calliper had stuck, all good.
 

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I am having my 12v battery replaced next week when I have my MOT.

The car is coming up to four years old in March, that seems to be from what I have read when the battery should be changed.

I keep getting a message about the battery losing charge when the car is not used, it's happening about every three days, too often for my liking.
 

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My nearest BMW dealer seems to cost more than most, I asked before I booked it in, and I was told £146 including VAT.

Your quote is cheaper!
 

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I am having my 12v battery replaced next week when I have my MOT.

The car is coming up to four years old in March, that seems to be from what I have read when the battery should be changed.

I keep getting a message about the battery losing charge when the car is not used, it's happening about every three days, too often for my liking.
What is the mileage on your i3 please? And is it used mainly for long or short journeys?

Useful information for others.
 

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The car is coming up to four years old in March, that seems to be from what I have read when the battery should be changed.
When I bought my car 2 years ago, I asked for the BMW diagnostics on the batteries. I got a printout saying the 12V battery 'performance' was at 98% and was fitted at 0 km. This means my battery is now 6 years old - still seems OK .......
 

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My problem is I do very low mileage about 2000 a year, some times it could be in the garage for a week and not driven, even more so at the moment because of the virus.

I need a car because of my disability, it gives me freedom and independence to get out and do my shopping and not depend on others.
 

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My problem is I do very low mileage about 2000 a year, some times it could be in the garage for a week and not driven, even more so at the moment because of the virus.

I need a car because of my disability, it gives me freedom and independence to get out and do my shopping and not depend on others.
When it’s not being used (in the garage?) do you keep it plugged in to the charger whether it be granny or 7kw?

Ours has not even done 500 miles since last March but as I said is always plugged in and when ever we need it it has been perfect.
 

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Holding the main HV battery at 100% for long periods seems like a much bigger downside than having to deal with replacing a £100 12v battery every 4 or 5 years, I have to say!
There's no reason why the 12v will be preserved any longer just because the car is plugged into the mains - as noted above the 12v only gets charged if the HV battery is charging, or if the 12v is already catastrophically low, by which point it's already degraded.
I think there's no good answer for this, car manufacturers will simply need to tackle this properly. Leaving the car plugged in to the mains isn't the answer.
 

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Holding the main HV battery at 100% for long periods seems like a much bigger downside than having to deal with replacing a £100 12v battery every 4 or 5 years, I have to say!
There's no reason why the 12v will be preserved any longer just because the car is plugged into the mains - as noted above the 12v only gets charged if the HV battery is charging, or if the 12v is already catastrophically low, by which point it's already degraded.
I think there's no good answer for this, car manufacturers will simply need to tackle this properly. Leaving the car plugged in to the mains isn't the answer.
But it’s not holding the traction battery at 100%.....no EV manufacturer in their right mind let’s the TB reach 100%, same as they don’t let them reach 0%......

Also when it is plugged in it balances the cells as needed keeping the pack at optimum.

I am sure you know better, but I will continue to follow the official guidelines.....
 

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Discussion Starter · #20 ·
I am sure you know better, but I will continue to follow the official guidelines.....
I agree; however, it has been suggested to me that the simple act of turning the car on (or just opening a door) is enough to start the DC to DC converter which supposedly continues to run for about 30 minutes after the car is locked. I confess that yesterday I decided to charge the tyres using an electric compressor. There are some reports that when doing this the DC discharge rate will exceed the charging rate so I confess that I powered up the car (making sure it was in park and handbrake on) and climbed out of the passenger door before using the compressor.
 
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