Originally Posted by wingnut60
He now has 6-volt batteries--what should be readings be on them?
He should first test them as a connected whole 12V battery. Assuming that his initial tests on the converter and wiring indicate proper charging operation...then the next step is to fully charge the batteries overnight and let them rest for 24 hours DISCONNECTED so there are no parasitic loads to impact a reading.
Then...if the batteries as a pair read BELOW 12.6V it is time to see if one or both are the problem. disconnecting the -/+ jumper between the batteries...one would then test each battery and expect a voltage of 6.3V or slightly more from a full capacity battery in good shape.
Usually batteries in pairs age together unless there is an actual individual cell failure in one of the battery... this would show up on a voltmeter pretty obviously as a measurement in the 4V range at best. Checking fluid with a turkey baster type hydrometer (10 bucks) can pin point the cell. One bad cell however can take down both connected batteries...so as WA8 suggests...it is a handy tool to have in your kit to be able to measure all 6 cells and insure they are aging slowly and together without needing to disconnect anything.