PayPal
AmazonThe simplest test of a battery's health is to see what voltage it is currently supplying. To do this set your multimeter on the voltage setting with the scale set to about 20 volts and connect the leads to the positive and negative terminals of the battery. A fully charged battery should show a reading of about 12.6 volts or higher.
A battery tester on a dead battery and a good one
On Pete's boat the old batteries were so flat they couldn't even power the tester, which doesn't always mean they can't be recovered. On a new battery, the tester reads the cold cranking amps against its rating and gives a state of charge and a state of health.
Why the voltage alone isn't enough
A battery can show 12 point something volts on a multimeter and still fail as soon as you turn the key. Watch the voltage while cranking: if it drops right away, the battery can't deliver the current. That's what a load tester checks, and newer capacitance testers do the same job.