i think it's the fob. Haven't tried charging the fob yet with wireless charger like some suggested to. Will update after i tried it

 

I just took mine apart... didn't use a dremel, instead I used a precision screwdriver where the key locks into the ignition (see side of fob) used some force (see: tap with mallet) then use screwdrivers to pry all the way around (remove key FIRST!).. to reseal I used crazy glue which left a white residue, there's an acid which melts the plastics back together but I cant remember the name...


the battery is soldered to the prongs, I didn't replace mine but doesn't look too difficult to pry apart and replace.