My car isn’t clicking over

I have a 2005 Jeep cherokeee , yesterday
afternoon I went and started my car it started
as normal drove down to the local store
came out of locks store and my car wasn’t
starting / started then turned off all lights and
radio come on and I’ve had no dash lights
come on , I was waiting for my brother to
help when I got out and tapped the battery
cables twice waiting 20 mins then my car
started as normal drove home , let it run for
abit then turned it off . My car then repeated
the same thing started then turned off and
not starting it’s got the revs etc to do it we
tested the battery and it was fine one of my
mechanic friends husband said it could be
the immobiliser? Looking for some help I’ve
just gotten another job and desperately can’t
have my car not running