CHARGING

Jon,  the best way to get to the bottom of this mystery is to get out your voltmeter or multi tester and see what your voltage is.  How old are your batteries?  Have you been on a good regimen maintenance wise like keeping the electrolyte levels up with distilled water?  Do you charge them faithfully once they drop to 12.2v (for a 12 v battery, 1/2 that for a 6 v.) for maximum battery longevity?  Let the battery(s) sit idle for a few hours and let them rest before taking a reading.   Then do the same thing a 24 hour period later.  The reading should be within 0.02v between the readings if the battery is good.  And yes, during the test, make sure it is disconnected from your pod so no phantom draws come into the picture.  Report back, there is your homework assignment Jon.

Good idea to monitor them regularity especially since they are always plugged in the chance of evaporating water is greater than when they aren't plugged in due to the charging cycle.