Hi River:
From the specs you listed, your batteries are not working correctly. When charging, your volt meter should show 14 - 14.4 volts. Fully charged, the battery should show 12.75 volts, and is exhausted at 10.5 volts.
If these are the deep cycle type, that have caps so you can check their water levels you should do so every week. The charging/discharging cycles boil a lot of water out of a battery.
If these are not deep cycle, they will burn out quickly. Be careful, many so called "deep cycle" batteries are not well made.
Check out the information on Trojan's battery site.
http://www.trojan-battery.com/Products/ ... hicle.aspx
Also, the battery connections can become corroded, which allows energy leaks. The connections should be cleaned, well tightened, and protected with your favorite battery protectant.