Load test a bank of 6 AGM house batteries.

AGM batteries CANNOT be load tested with a standard Load Tester. You must have a Load Tester that is designed for AGM batteries. You need to state how OLD the AGM's are. As another poster stated, when you engage the battery boost, it uses the COACH batteries to close the jump solenoid. When the engine is running, it uses a Ignition Chassis signal to jump the Chassis and Coach together at that Jump Solenoid. AGM batteries are great if taken care of. AND when they get old and worn out they will fail with no real warning. From your description of you problem, your AGM's are bad/worn out. You ALWAYS replace ALL batteries in a Battery bank. NEVER just replace any that test bad and leave the ones that test good/marginal, especially AGM batteries. If you have 6, I would bet they are 6 volt and not 12 volt. But, some Large Motorhomes have 12 volt AGM's. Especially since you state the larger 10k Genset. Doug