To further the discussion for those who haven't had the pleasure of being driven crazy by battery problems, your gauges may show voltages of something like 13.75 volts. Maybe higher.

Those are charging voltages. On a typical 12 volt system it is not unusual to measure 14 or 14.25 volts. There is a range of voltages your battery sees especially when connected to more sophisticated charging systems. Think of charging voltages the same way you think of the pressures required to put 100 PSI of air in your tires. You could get your tires up to 100 PSI if the air hose had 100 PSI in it, but it would seem to take forever. So instead you use a hose with 125 PSI (or more) to fill the tires to 100 PSI. Same with your charging system, except there is a limit to input voltage so you do not damage the batteries.

The voltages Jeff posted are of a battery at rest, with no charging circuit or loads attached. And most importantly the voltages are after the surface charge has dissipated. That usually takes several hours.

If you have any questions about your batteries or battery charging system you will only need a cheap multi-tester, and information such as what Jeff posted.

To increase your battery life never ever let your batteries discharge deeply. If you start your generator and charge your batteries every time they drop to 12.5 volts your batteries will outlast those that have been allowed to routinely drop to 12 volts or less as some auto-start systems require.