So I put a spare FSR last night and took the Ctek charger off. 50a fuse went back in.. Fan didn't come on and it started OK this morning. I will use it and then leave it for a few days on the drive to see what happens.
Tell you what tho - I'm glad I bought a jump starter pack last year. Topdon is the make but can't remember what power output. They are so handy. Highly recommend getting one.