Charging keeps blowing circuit breaker

Owner's manual:

 

I have always charged my car via a GFCI breaker and have never had an issue. depending on how things are wired it can be either the car, or something else downstream of the gfci (again, depending on how it's wired) that's causing it to throw...

or it can simply be a tired gfci

 

Same thing happened to me. I replaced my 20 amp GFCI which kept tripping to a 15 amp GFCI yesterday. I believe the Prius uses 16 amp. Solved the problem for now.

 

It uses 12A on the 120V charger it came with.

 

Yep, resurrecting an old thread. Car draws 12A @ 110VAC and 16A @ 220VAC

GFCI plugs do go bad and are engineered to pop open, rather than fuse shut. That would defeat it's intended purpose. The same goes for your panel circuit breakers. When they are going bad they will pop below the rated capacity, again safety is it's intended purpose.