RV Repair: Batteries, volt batteries, rv repair

Question
How can I test my battery condition? I have 4 six volt batteries linked up in 2 in a series. Recently I noticed my converter working over time, which usually happens when one or more of my batteries is low on water. (When my converter works over time it heats up, turning on the cooling fan.) I isolated the suspected 2 batteries and soon sfter the fan turned off. Now I have to figure out which of the two, if not both, is going bad. They each checked out with 6 volts but that doesn't tell me if their is a problem or does it? Am I going to have to take them out of my RV and into a service dept. or is their another way to tell?  

Answer
Keith,

     To properly test the batteries you will need a hydrometer to check the specific gravity of each cell and a load tester to remove the surface charge.  You probably don't have these tools or you wouldn't have asked the question, so yes you should remove them and take them to an RV repair shop to be tested.  When replacing batteries that are connected it is recommended that all of them be replaced if there is more than a year of difference in the age of the replacement and the existing batteries.  This is because a battery slowly loses its ability to reach full charge.  If you only replace one battery the other batteries will constantly pull it down to their level, decreasing it's life span considerably.  I hope this helps.

Darren