Mini Cooper S Convertable 2005

Mini Cooper S Convertable 2005

Approx 2 years ago , my vehicle had just been serviced I was overtaking when I lost
acceleration, none at all even though car was still running. Same thing 2 months ago and
then a week ago. Yellow light appears on the dash.

So a few weeks ago I see the same light on and decide to power off the vehicle and
restart, nothing, battery died on me. They yanked the battery out and replaced with a
"Dixon" and assured me it is an excellent battery, I have learn't this is not the case (Not for
Mini anyway) They never put it on a computer to do a reset, I learn't this later.

Since then my rear windows and roof wont drop, checked that the panel is correctly
seated in the boot. My lights come on the minute I power up the vehicle and don't go off at
all. At the last test 2 weeks ago my battery charge level is sitting @ 12V in idle. I was told
my alternater is fried, however she has been running like this for 26 days and starts up
perfectly.

Any possible clue as to what could be causing this? Could it be a faulty/poor battery
causing these issues? 86 000kms on the clock, full service history.