[Putershark]

Batteries can show good voltage, but not enough amps... Their are a couple of ways to tell though without having a load tester handy.

1. Feel the sides of the battery and see if you feel a bulge, usually a good indication of a shorted cell.
2. Hydrometer test is pretty simple and a low cost tool as well as being pretty accurate. Test each cell (if the water level is correct) and measure the specific gravity for each. If found low on water which is very common here in the Florida heat which usually kills unloved (un-watered) batteries in 3 years or less... Just put in some distilled water and put on a low charge overnight then re-test.
3. Use the engine as a load tester... If it cannot start the engine several times in row without getting the click of death, time for a water level check and overnight charge. If still acts the same, time for a new one...
4. Take it out and run it by any auto parts store. They pretty much all have load testers to check them.

Dave your issue though could also be a simple loose ground or connections that are loose behind the battery switch if you have one... Loose connections on the back of the A-B switch has burned me more than once! Well, at least till I got smart put some lock washers on them