Battery seems to be disconnecting

So the night before I was parked waiting to
pick someone up from work and had the
engine off but the battery running for the
radio. When I turned the engine on the
radio had been shut off but the disc
changer was shuffling through the discs on
its own and this went on for about a
minute. It finally stopped and it seemed
fine and went home. The next morning I
was able to unlock the car doors with the
key via the button but when I went to turn
the engine on everything was shut off as if
my battery had died. So I went back in and
decided to ask for a jump later on. When I
went back to check on the battery an hour
later everything was on as normal and
when I turned the engine on there was no
stutter as would happen with a dying
battery. I went and turned it off and
decided to try again in an hour. Everything
worked fine so I decided to head out and
fill up my gas tank. At the gas station when
I got back in my car the same thing
happened again where everything was
shut off. I check the battery again and the
circuits and everything seemed fine so I
got back in and everything was on again. Is
there an issue with the battery,  a lose wire
or is it something else?