Wanderer 1967

Just obtained a 1967 wanderer. Replace the batteries. Have 3 12 volt lawn mower batteries in parallel. When I attempt to use power lift system it blows a 20 amp in line fuse in the wiring to the lift motor. System works great if I by pass the fuse.
Should there be a 20 amp fuse in the wiring to the lift motor?? I would assume since the motor is a starter it. Would draw more than 20 amps??
Are three batteries in parallel too much amps??
I am not an electrician. Help on electrical is needed and appreciated