Re: Enging/starter battery pretends to be good but....
Did your crew chief ever say something like "All you fly boys better bring my airplane back in one piece!" ?
If the battery is good and the engine won't start, the diagnostics are always the same. Check battery, check wiring, check starter. One or more of those will be bad. If you get it to the point where the starter spins up the motor but it just doesn't fire up--then you've got engine problems. If it doesn't spin up:
Check battery, check wiring, check starter.
Quick check, carefully use jumper cables to directly connect the starter to the battery. If it spins up, you've got a wiring problem. Loose or corroded wiring usually. If it doesn't spin up--off the starter goes for a bench test.