Well... about a month after I bought it, she wouldn't start. I got a jump-start, but at the end of the day she was dead again. So I charged it up and she was fine for a few days, then dead again.

Took it to a few garages who said the battery wasn't holding the charge. They tested the alternator too. So I replaced the battery with a Bosch and all was fine...

Then about a month later it was dead again.

I thought it was due to me only driving 1.5 miles every day, as this may not be enough to replenish the charge used to start and run (with the heater and Webasto) each way as it's pretty cold in the UK a the mo.

But then a few days ago, I parked up in our underground carpark, and 2 days later it was totally dead; had to use the key to open it, then had to connect it to my running M3 for 15 mins before there was enough power for it to even crank over.

One thing I had thought though was that the car-phone (Motorola V50) is always plugged into the armrest, and never used, but possibly always on charge? So I've unplugged that to see...

Last night, I took some measurements with my multi-meter:

—no draw, engine off, 12.55v
—no draw, engine on, 13.75v
—draw (blower, lights, nav), engine on, 13.75v

I also checked what the current draw is when she's powered down: