2018 cherokee wont start
 

A short time ago, I had an auto start/stop fault. Then I quit working all together ( meaning that it was on but there was no fault and the engine didn't shut off at long stops). Then yesterday while I was running errands, I got in to start it and nothing. Dash lights come on, no apparent electrical issues, key fob battery is good, shift lever is in position. Someone tried to jump me but still nothing. I about gave up and all of a sudden it started. Went home and shut it off. Now it won't start again. Battery is 12.4. I try to remote start and get 1 weak beep. Battery seems good but I figured if it's a battery issue, it would have started when jumped. Suggestions?

12.4V is low for starting, batteries need to be load tested not just voltage. There could be several problems and it would be best to get codes read if a good battery will not start. Jump leads connected donor car will need to increase their revs depending on condition of their battery and alternator.
A worn out starter motor will drag more amps than it should and can stop ignition on petrol cars, but start with basics first
Hope you get sorted soon, good luck.

I just replaced my main battery about 8 months ago because of it producing under 14.3v. It took one jump and then would not start even if jumped. Replaced battery and all is good. Got a sh@t load of error messages as well when the battery went. Original battery was only three (3) yrs old. Good Luck.