Lesterbmwi3 said:
In May 2021 my 12 v battery will be 7 years old I check once a week before I start a car through cigarette outlet with modified voltmeter is still 14 ,5 volts all the time I charge a car at list once a week and in 7 years I drove only 20000 miles car is always in 60-65 “ garage I use heating or AC very seldom only radio and I lock a car in garage and on displays showing any lights at all those parasite discharge is not there just wander why I don’t have any problems with that 12 v battery Right now I ordered any way 12 v battery OM from dealer $191 already waiting 3 weeks they must ship from EU I must be lucky my battery last so long . After I get my car nobody mess up with programming or up dates maybe is still functioning so good figure out . As so many owners complains about 12 v battery and I still can make 70 -75 miles from that go cart which factory range was 84 miles
The day your 12 V battery fails, your auxiliary power port voltage will still be ~14.3 V because that's the output voltage of the DC-DC converter that charges the 12 V battery, not the voltage of the 12 V battery itself. I installed a voltmeter in the auxiliary power port of our 2014 BEV more than 3 years ago hoping that it would display the voltage of the 12 V battery as an early indication of a 12 V battery failure. Unfortunately, unless the voltage of the 12 V battery is pretty high (i.e., a high charge level), the DC-DC converter will turn on to charge the 12 V battery. Because we drive so little, the average charge level of our 12 V battery must be lower than normal. A low charge level warning has been displayed once, so I charged the 12 V battery with a battery charger. During the pandemic, I've been driving only ~100 miles/month which seems to be insufficient to keep the 12 V battery charged, so I remotely unlock then lock the doors which turns on the high-voltage system for ~30 minutes during which the DC-DC converter will charge the 12 V battery, if needed. I wonder how many good i3 batteries have been needlessly replaced when all they needed was to be charged.
A better way to monitor the 12 V battery would be to install a wireless battery monitor that measures the 12 V battery continuously, even when an i3 is off and parked. That might show the battery's voltage gradually dropping as it ages, or maybe its capacity decreasing which would result in a lower average voltage. However, a monitor would add another parasitic load, although small.
The 12 V battery in our 2014 BEV is the original battery that continues to function normally. Our i3 has had its system software updated 3 times by our BMW dealer and is running the November, 2018, version. I have changed several behaviors using BimmerCode. The parasitic loads of the telematics module, the keyless entry transceiver, the entertainment system clock, and the burglar alarm, if armed, can't be avoided.
A couple of years ago, I ordered a replacement from a local East Penn Manufacturing retailer as a result of so many owners of older i3's reporting failed 12 V batteries. I didn't want to be stuck buying a replacement battery from our BMW dealer had our battery failed. It's still on a shelf waiting for the original battery to fail (I charge it a couple of times each year). This is the same battery that BMW installs in North American i3's and can be purchased for considerably less than $191. This battery is manufactured in the U.S., so your battery shouldn't be coming from a European country.