you need to test not only for voltage but current capacity.

set meter at something above 15 volts dc and check disconnected
battery. shouuld get at least 12 volts or thereabouts

now connect battery plug in device, check voltage again, should be
around 13.8, the voltage the battery charges at.

now let us know what you find and feel free to e mail me


batterys last only a few years at best, yours are probably both bad