BMW E39 530i Trouble starting the car...?

[german k]

so today i decided to clean the whole car inside and out, while doing this i had the windows down and the radio on, after a while the radio turned completely off and wouldn't work even if i pressed the on/off button again and again.. so i tried turning on the car .. wouldn't work so i figured the battery was almost dead.. so i ignored it for a while till i was done w/ the whole car and while i was polishing it, the alarm went on and so i pressed the unlock and then the lock button to shut it off.. and this happened a couple times. then i called up my dad who brought the other car to jump start my bmw but all it did was turn on the alarm, then we turned the alarm off and then i tried starting up the car but it wouldn't let me... also the emergency lights went on when i tried starting the car.. and the dashboard kept on dimming and lighting up and then dimming again...( we first jumped the car from the cigar thing in the car) then we tried the battery that was all the way in the trunk of the car ... and it didn't work either.. now we haven't used the car in about a week or two .. so then my dad said... it's probably the key that's almost dead and that's probably why the car's not starting (supposedly there's some kind off id thing in the key that the car can't read w/out the key having battery life...) but other than that... what would be the problem?