Cannot open back and warning lights stay on even though no key in ignition

I left the key in the ignition of my 2011 ML 350 for about 2- 3 hours.   I assume the battery is dead, but I cannot open the back of the car and there are warning lights lit up on the dash even though the key has been removed.    I'd like to try to get to the battery, but cannot since I can't open the gate.   HELP!  :-)