What would my next steps be for the following?

I have an 2006 X-3 with an extended warranty. It has about 35K on the odometer. I try to drive it 1-2X a week. When I do not drive it for over a week I put a trickle charger on it (1 AMP). The vehicle has not given me any problems other than a battery failure last year 3,000 miles back. The dealer was pleasant at the time stating that the battery was covered under warranty and promptly replaced it. Its been starting fine up until last week when I noticed that the battery was dead (eye=black) again. I went to the dealer this morning and they said something was draining the battery - looking at my telephone cigarette ligher charger (which I do not leave in the car) blaming that for my problems and stating that I would have to buy a new battery ($200) and install of said battery ($100 and change) and the replacement battery was not covered.

I mentioned to the SA about reading about similiar battery issues with the X-3. He said he did not know of any issues relating to the battery.

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E83 - Aero PKG Mods installed: Homelink mirror. CIS-IBUS video module, AUX, Rr Dr Release, stock wheels, Remote start, CarPC (Atom) & mud flaps - NAV - MKIV - NA Map DVD - 2011
E46 - 18.5 wheels/tires (summer), 17 stock (winter), Homelink, NAV software upgrade, BMW video module, Radio to V53, AUX, USB IBUS interface,BMW alarm install, CarPC(Epia), remote starter, tank battery & angel eyes. NAV - MKIII - NA Map CD - High Version 2008.1