The starter itself makes a pretty good battery load tester. Disable the ignition system (or just don't turn the ignition on with a stomp starter) and crank the engine for 10-15 seconds with a voltmeter on the battery terminals. After 15 seconds, and still cranking, a good 6 volt battery will still be showing 4.5 volts or more at the battery posts. Subtract 0.2 volts for each cable connection between the battery and the starter with good cables and tight connections. After that much cranking time, let the starter cool down for at least 20 minutes before cranking again.
Jerry
