Help my car has got a bad gremlin!!!

[The Chad]

Ok here's the problem:
Car: 1995 240SX

-I was walking to my car 3 weeks ago, used my clicker to unlock the car and hopped in, went to turn the key...NOTHING, i mean no working clock, windows, all power gone.

- I figured the battery was just dead? , so i jumped it and no problems.

- Got the battery checked at Autozone just in case, everything was fine.

- Same problem occurred 2 days later, so i checked my ground for the battery. (I had relocated it to the trunk a few years ago)

- Ground wire had a bad connection so i replaced and regrounded to new spot on frame.

- Worked great for about 2 weeks, then back this morning...did same thing... no start or power to anything!!! ....but came back out 30 mins later and started right up like a new car!!! :/

- Checked the ground for the battery again and everything was tight.

- I cant figure it out!!!!, Is there another major ground that I should be checking?? Any help would be much appreciated. Thanks in advance!