A couple of times in the last month I saw something like a "battery discharged" message appear and then go. There may have been a slight hesitation with starting but this was very infrequent and I had no issues. Fast forward to a gas station lineup yesterday where it wouldn't restart and I needed a boost. I drove the 5 or so km home and at that point my multi meter said I was at 12.4v.. Mini service says you have to drive these cars a lot to keep the charge up which was a similar line to what the BMW dealer told me about my old N63 5 Series and that I should put it on the trickle charger. .He said there is actually a "replace battery" message that comes on if its pooched.

Anyways after a few hrs on the charger it was up to 12.85 so I disconnected. Today I checked its down to 12.55v unstarted. Does this seem to be the sign of a failing battery or is it within normal parameters to drop that kind of juice over night?-

Anyone?

 

A failing battery might still show 12+ volts at rest, but when put under load will discharge faster than when new. That’s the real test, discharge rate.

 

Yes I am not comfortable with unexplained gradual leakage At 5 yrs I think I will replace as step 1 and if there is still an issue I will have only discarded a battery with a couple years of reliable life remaining.. I am a little choked about the labor necessary to switch the battery out though. I think burying a battery like this is an attempt to discourage even basic self maintenance like the $400 BMW oil change.

As always, appreciate your tips Nik.

 

Changing the battery isn't as bad as I expected, just takes a bit of time to remove the components surrounding it. Certainly not as easy as the 5 minute job on my Mustang, but not 'horrible' either. Don't forget to register the new battery to the car, so it doesn't get slapped with excessive charging voltage and shorten the life of the new battery. Just another fun detail of today's newer cars trying to eek out every last MPG for ratings. Our cars have a lot of electronic circuits that 'snooze' when not in use and will activate when the fob comes near or if you even open up a door, like pump priming and systems checks. Loosing a few tenths of a volt overnight doesn't sound all that out of whack. As noted, voltage can be fine, but if you don't have the capacity behind the voltage (i.e.- during startup), it doesn't give you the full picture of a battery's health.

$400 for an oil change, heck my local dealer only quoted $185...they are obviously missing out on a lot of profit potential... Beyond the original 3/36 free maintenance, my Mini has only seen the dealer for the extended warranty shifter replacement last week. Of course they quoted a few other service items while the car was in...which I politely declined. My passenger engine mount has just recently died, based on the fresh mount oil on it...that was a mear $965 quote. I am quite sure it won't be as involved as the oil cooler housing replacement I did last winter...hard pass.

 

Yep pretty much the same here.


1. +1 register the new battery with a scan tool. I did mine with the schwaben tool.
2. load charge it, as even with 12v it might have a bad cell.