battery drain in my X5 4.8 (2007)

This is a post I made earlier with a possible water/short relavance

My 2001 x5 has always had strage issues with the lowest of the three tail lights in the tail light assembly on each side. The light on the dash would often go on intermiently signaling there was a problem back there on one side or the other or both, but i had replaced the bulbs too many times for that to be normal. Then I started to notice it occured especially after a rain storm or a wash. Upon removing the whole tail light assemblies, i noticed the the little metal flat connectors for that bottom bulb had been burnt, like they were shorting out. I surmised that water had soaked up in the neopreen seal that extends over the metal connectors and had therby shorted the circut by serving as a connector. Anyway, i cut back the sealer so as not to continue the problem, and everything seems fine... except that the bran new battery i just bought, ran out of a chrarge after three days./

The exact same thing was happening to my previous battery recently, and it had been working fine for around four years. Of course I thought the short had something to do with it, but i didn't know exactly how. Plus I fixed that short and put in a new battery, and it hasnt even been wet--and yet my new battery is not getting charged. Could it just be co-incidence and i just have some other problem. the acessory belt seems fine and tight. Anyone have any clues for me?

Bought an ex-stock BMW about 10 months ago (my first venture away from Toyota) and everything has been great until...
I left a USB memory stick plugged into the central console for several days.
- THEN I started to get 'high battery drain' errors followed by the service light coming on.
I took it to the dealer who checked things out. They blamed the tracker device!
- BUT this is when they found out the car was fitted with 2 trackers, mine, pulling 60-80ma when awake and a BMW Trackstar pulling 250ma, that they didn't know about when they sold it to me(?).
- SO my tracker company came and checked the device, all ok. They did move the connectors to a continuous supply but this should make no difference.
- The dealer said I needed a new battery quoting £356 quid, for a warrenty car.
- RESEARCH - my tracker monitors the battery - it hadn't dropped below 12.2 volts!
- An INDEPENDANT battery check was undertaken - it's fine and would only cost £95 to replace!
- SO - I'm about to plug the USB back in for a few days to prove or disprove my theory - wish me luck......