Here here,
I know that you can buy a CTEK conditioner over the counter at BMW, its exactly the same apart from a lovely BMW sticker on it. Turn the charger over and it has CTEK stamped on it, I believe BMW charge £50 ish pounds.
Mine is just sitting in the garage on trickle at the moment, saved me spending £100 for exactly the same problem.
If you need the part number let me know.