12V battery failure

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johc
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12V battery failure

Post by johc »

Our 2015 i3 (Rex) suddenly started displaying the error message "Abnormal discharge - please run engine as soon as possible". No other information was provided. At the time the battery was about 95% full, so it was not possible to get the Rex to run (battery apparently needs to be less than about 75%). We had a longer trip planned for 2 days after the message started appearing, so thought we would use that trip to run the generator. However, on the morning we were planning to leave, the car was unusable. Initially it appeared that all the warning lights were on simultaneously, and the car would not run. The parking brake could not be disengaged. We left it for half a day and had a similar experience on attempting to restart, but, after a couple of attempts, all power was lost - no instrument lights, no cabin lights, nothing. BMW emergency roadside assistance could not be raised, despite it being about 3 pm on a Saturday afternoon. The car was transported to BMW Sydney, who identified the problem over the phone, and have since replaced the 12V battery (cost approx $800, plus transport from Wollongong to Sydney).
Fortunately the car was at home when the meltdown occurred, but this happening on a trip would have been much more of a problem.

i3 owners should be aware that "Abnormal discharge - please run engine as soon as possible" could mean imminent failure to proceed.
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coulomb
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Re: 12V battery failure

Post by coulomb »

johc wrote: Mon, 13 Jul 2020, 20:23 error message "Abnormal discharge - please run engine as soon as possible".
Perhaps this is a copy and paste error from an ICE ECU, where what they really meant was "turn the car to ready as soon as possible" (to charge the auxiliary battery via the DC-DC converter). In an ICE, running the engine would of course charge the 12 V battery via the alternator.
... have since replaced the 12V battery (cost approx $800, plus transport ...
Ouch. That's a gold plated auxiliary battery. I hope it's better than an automotive starter battery. A good AGM battery from the right supplier is around $200, plus about 5 minutes of labour to put it in.

Edit: it's a little ironic that one of the vestiges of the internal combustion engine, the lead acid auxiliary battery, is one of the least reliable components in an electric car.
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brendon_m
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Re: 12V battery failure

Post by brendon_m »

coulomb wrote: Tue, 14 Jul 2020, 11:07
... have since replaced the 12V battery (cost approx $800, plus transport ...
Ouch. That's a gold plated auxiliary battery. I hope it's better than an automotive starter battery. A good AGM battery from the right supplier is around $200, plus about 5 minutes of labour to put it in.
Your paying for the speciality of the battery and the BMW factor.
The battery in 'stop start' cars are also special because of the way they are worked and they cost about $700 (although strangely they used to be cheaper...) and last a few years. Sort of takes the edge off the fuel savings...
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brendon_m
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Re: 12V battery failure

Post by brendon_m »

I looked up the 12v battery in the i3 teardown courtesy of Munro and associates.
It cost BMW an estimated $32.50usd for the battery. I'm guessing there's quite a few middle men getting their grubby little paws into the pie before it ends up being fitted into someones car at the dealer for $800 :o

Im mean, I'm fine with suppliers taking a bit of profit along the way, they have to eat too, but there is a point where it is just extortion.
Peter.Gorton
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Re: 12V battery failure

Post by Peter.Gorton »

My 2014 BEV 12V battery failed earlier this year, at about 65k km. Lots of warning - nothing actually saying that. As the vehicle wasn't being driven as usual, virtually every day (lockdown), the old battery eventually failed (not getting topped up by traction battery when driving).
Replacement from BMW was less than $400, and 30 mins to fit. Genuine battery is a drop-in replacement - not requiring BMW to recode it (as per some earlier youtube posts).
Be aware that BEV has 20Ah battery, and REX has 40 Ah, which is larger physically, and won't fit BEV tray.
All good.
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