250m Ho problems. (bad job of rigging.)

My friends 250 HO was giving him all kinds of problems. Bad hole shot, slowing down at hig rpms, loss of low end power. When put on diag. software would give all kind of readings as motor problems( thought comp. was bad.. It appears( not sure yet) that his problem is the "factory" that rigged his boat put a 600 cold cranking amp battery in the boat. If that is the problem that backs up the old theory us old guys had about less motor care from your local dealers if the factory got most of the money for selling the boat as a unit with motor. dealer has a tough time these days and i can see why it is hard to keep high quality mechanics on these new motors.