Part of battery maintenance, a couple times a year you might want to "equalize" them each separately by using your Motomaster charger and letting the voltage come up to around 14.5 for an hour or so if you have a manual mode on it. Vigourous gassing will "swirl" the electrolyte to mix with the distilled water you added. After letting the battery sit for 24 hrs, no load, check the voltage, should be at least 12.65 to 12.7. Ensure the tops of the battery and around each post is scrupulously clean, anything on there can cause a slow discharge.
Just for S&G, I went out and looked at my RV battery, June of 09 and still strong.