My battery died. When I measured with multimeter it showed 0v. I used NOCO car battery charger to charge the battery. It whent all the way to 12v+, but then went down to 8.6v and stays there. Does that mean the battery is bad? How come it stays on 8.6v and doesn't go to 0v? I thought if the battery is bad it either doesn't charge at all or goes back to 0v.

 

That means the battery is bad.

 

two cells are dead, replace the battery

 

Yes.
Exactly what @A383Wing said.
Although it's been 2wo + years now; I had this same instance occur with a battery, as you.
My battery was nearly, only a year old ("Autozoned" purchase) and began having issues. Tested @ 8.5 volts. Warranty was honored.

 

I just had the same thing happen to my Genuine MINI Battery i got in 2018. When the MINI sets for a long time even with a trickle charger on it, seems like their life is cut in half, when i drove the car year round the first battery lasted like 10 years. Now its like 3-5 years

 

Thanks for that ECST.
I also found it odd that when we purchased our 04 R53 new - the original Mini factory installed battery (driven everyday), completely died within 1.5 yrs of our lease. As did the alternator shortly/months thereafter. The replaced battery lasted a good 12+ yrs w/no problem. As did the alternator still present (16 yrs), to this day.

 

Yep, just did mine the other day and its back in action. Hope to have it all done and back on the road.