electrical issue

i have an 04 cayenne, sometimes the car wont start and i have to let it sit for a while then keep trying and it will start. also the remote doesnt unlock/lock the car. this morning i got in the car and it was dead wouldnt even crank. i checked the voltage at the jump start ports, 2volts. i got it jumpstarted, while running it was showing 14.1volts. i let it run for about 45 mins then shut it off again while still monitoring voltage, found that it stays at 12.6 volts when i shut the key off, then about 5 seconds later theres a click under the drivers seat and the voltage drops rapidly down to like 3v. but then i put the key back in right away and it jumps back to 11.8 volts or so. i got access to the battery under the seat, jumped the car again and watched the voltage at the battery itself, when i shut the key off it did the same but this time i unhooked the ground cable of the battery and let it sit, after 40 mins the battery held 11.9volts. it has an interstate battery that was put in 11/09 but if its holding voltage the battery cant be the problem right? any ideas? common cayenne problems?? thanks