could be that your battery charger has a reverse polarity protection facility, so if it detectd that you have connected the charger on the wrong terminals, it might not have been charging the battery, which in turn, when you went to jump start it initially, the battery would have needed a while connected to the helper battery before the car would start.
My mini had been sat for about 6 weeks without being started and the battery was totally flat. Took about 5-10 mins of being connected to my van on fast idle for enough current to even turn over the engine.
Edited by M44K TS, 06 April 2008 - 10:37 PM.