Possible stereo wiring issues. Startingissues

So my cavalier has been having issues since I
installed a new stereo and amp as well as installed
2 10' led strips.  The issues started with the music
being sodtorted due to the fact that I did not have
an aftermarket stereo harness for the stereo. Then
it led to the light gauge flickering when shifted
from P though D u less the beams are on.  Then
one day before o got the harness I left the car on
accessory with the fan on low and with the stereo
on low volume while I was parked at a pump while I
went in to pay for gas.  I was 4 minutes maybe and
I pumped $10 of gas and went to start the car and
it just made a clicking that sounds so be near the
battery on the left side of the front.  The lights
worked and and the stereo worked but the car
wouldn't start.  So after disconnecting the battery
terminals and connecting them again I tried to
start the car again a couple times and it started up.  
Ever since then the car car has had some started
up issues. Sometimes it will crank sometimes it
clanks as if the battery is dead. But I don't think it
is the battery. Any idea what the problem could
be???