Battery or Alternator?

[imi7]

Would be grateful for your advice on the following issue please:-

Background: replaced the battery and alternator at BMW dealer back in March 2012.

Current: Left inside light on for 2 days and came to open the car - everything completely dead !! Trickle charged it overnight, and during this charge could see the car coming back to life slowly (opening doors activates inside lights etc). In the morning, after a good 10 hr trickle charge, started car and got the usual warning lights on the display - these cleared immediately with right/left steering lock.

Anyhow, now thinking car is ok I unhooked the trickle charger and let it sit for the day. Came to the car in the evening and it started fine. But, when I switched on my aftermarket HID fog-lights the hazard lights started flashing and inside light came on - car still running as normal and no warning lights on the dash at all (I have had these HID fog lights for 2 years now with no problems). I unlocked the OBC to check the voltage - Car not started voltage is a steady 12.5V, upon starting car dips to 9V (ish) and then gradually climbs to maintain 13.5V. So I put on the fog lights and Voltage dropped to 12.4V then climbed back to 13.5V - at this point hazard lights flashed and inside light came on (simple fix was to turn off hazards and inside lights and continue driving as normal). No additional warning lights on the display - drives perfectly ok.

So - would you guys put this down to the battery being no good as it was totally drained (have not checked the physical battery condition yet), or could it be something else? how long should I need to trickle charge it for it to be 'healthy' again?

On a side note...the bloody coolant started leaking. Was thinking of selling the X recently but going to have to spend $$$$ on it repairing stuff so gonna keep it. Just put on 2 new rear tyres and replaced control arm bushes - sly thing has its own way of staying with the family .

Thanks for any help received.