After 15 seconds of cranking with the ignition disabled, a good 6V battery should be at 4.5 volts or slightly above, while the cranking load is still on the battery. Have a helper push the starter pedal while you hold a set of voltmeter leads directly on the battery posts- - - -NOT the terminals bolted to the posts!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!