Inspect the battery for damage. Look for fluid on or around it to indicate if it is leaking. Replace any leaky battery. Check for damage and good connections on the terminals, connectors and cables.
Look for corrosion and clean it off with a warm water/baking-soda mixture. Use 1 lb. of baking soda for every gallon of water. Use a post and clamp cleaner to clean the battery terminals and the cable clamps on their insides.
Check the battery's electrolyte level on a monthly basis. Check it every 2 months if you leave the RV plugged in with the converter battery charger charging the battery.
Add water by removing the vent caps, checking the electrolyte level and using distilled or another mineral-free water. If the level is below the plates, fill it just until it covers the plates. Add no extra water until the battery is charged, then fill it no higher than 1/8 inch below the fill well.
Test the battery's state of charge by measuring the voltage with a digital DC voltmeter. A 100-percent state is 12.73 volts for a 12-volt battery and 6.37 for a 6-volt. Seventy percent is 12.37 or 6.19; recharge the battery if it is below this level. Don't discharge a battery that is below 40 percent (11.96 or 5.98).
Use a three-stage charger if possible that gives the battery a bulk charge, absorption charge and then a float charge. Use a charger whose charge rate is between 10 to 13 percent of your battery's 20-hour AH capacity.
Recharge the battery immediately after use. Charge it in a well-ventilated area with no sparks or flames around. Check the electrolyte levels before and after you charge the battery.
Disconnect the batteries and store them if you are storing the RV.
