My 08' Yukon randomly will not start (more so in the winters cold temperatures, 32 degrees or below) and the 12v battery is drained so I have to jump the battery for it to start. I then could go for a few weeks with no issues. I'm only getting an avg. of 13mpg fuel economy. I have also noticed when it rains out, these issues of the car not starting and the 12v being drained occure almost everytime it Rains too... the car will also randomly rev up to higher RPMs at 20ish mph, this has only happend right after starting the car. Any ideas on what is going on?

 

Bad 12V

 

also should have mention to make sure the cables are snug they are known to "come loose" on the 08 09 this could cause resistance leading to a dead battery or low charge situation