While a faulty breaker is possible it is probably doing just what it is designed to do. A loose hot or neutral connection won't trip the GFCI unless it is leaking current to ground. Turning 1 circuit on at a time is good advice. If it is your charger circuit I would remove and bench test at local shop. When GFCIs first came around there was a lot complaining about tripping circuits, most of the ones I saw the tool or appliance was leaking voltage to ground and fixing or replacing fault at the tool fixed the problem. Remember GFCI can trip at .003 amps but .005 can be dangerous. By the way it is good to check the 'test' button on GFCIs since they can fail to trip. A fellow on a job I was on 3 years ago was taken out in an ambulance after a faulty ground fault did not protect him. I made my living as an commercial\industrial electrician for 40 years.