No electrical power after being park five minutes

I drove to mom's house a half a mile down the road. Got out locked the doors with key fob. I was in there no more than five minutes. Came back out and unlocked the doors, stuck the key in the ignition and tried to start it. And it has no power, no lights on, dash comes in and the interior lights will not come on. Even the power locks won't lock or unlock. I did not leave the headlights on or any interior lights on. What could be the problem?