Parents have a Craftsman 21" Self-Propelled Lawn Mower with a Briggs & Stratton 6.75 hp engine (125K05) with electric start. 4 years old. Original battery is putting out about 13-14 volts. Sometimes starter will just spin. Every now and then starter will engage, but will not spin engine. Even when starter spins, it seems weak. Should we replace battery, replace starter drive, or replace starter? Engine starts fine with pull rope.

It seems like you may need a new battery. You should test it though before you do.

It seems like you may need a new battery. You should test it though before you do.

Thank you for your reply, Hailcanadien! I did check the voltage and it was OK. I don't have equipment to do a load test. Any other way to test the battery? This is a small, sealed lead acid battery.

Does the starter need a specific RPM for the drive to engage? I am assuming the drive relies on centrifugal force to engage.

Update. Using jumper wire I connected the starter to my truck's battery. Starter turned the mower engine properly. Appears mower battery lacks sufficient cranking amps. Ordered new battery.