I had fluctuating voltage on my 2004 Cooper, 12.5v for 20 seconds then up to 13.5v for 10 - 20 seconds then it'd drop back, battery light comes on and off. I assumed new Alternator required, got a new one fitted. Same problem. Is there anything else that can cause this or have I been unlucky and got a new bad alternator?

__________________
This post was auto-generated based upon a question asked on our tech article page here: MINI Cooper Alternator Replacement (R50/R52/R53 2001-2006) | Pelican Parts DIY Maintenance Article

I've seen a few bad new alternators BUT it's rare. Double check the integrity of your field wire and check for corrosion on the big B+ lead connections. Also verify that you do not have a voltage drop issue between the alternator and the battery by performing a voltage drop test between the B+ terminal on the battery and the big connection on the rear of the alternator.

- Casey

What did your battery test at? Is your power steering making any noise? Any fluid leaks under the vehicle? When a P/S pump goes bad it can cause draw and the battery light will aluminate. Has yours ever been replaced? Does your P/S pump fan kick on when the AC is on? There is an extended warranty for the first gen MINI power steering pump.

MINI Cooper Power Steering Pump Replacement (R50/R52/R53 2001-2006) | Pelican Parts DIY Maintenance Article