I remove and top-up charge. I put them in an unheated shed but a basement corner is good. I check them to see if they are charged each month and then recharge as necessary using a 2 amp charge. Batteries keep best fully charged or close to it. BTW a plastic cap for the + terminal prevents accidental shorts should a conductor fall across both terminals. The caps can be purchased at most auto parts stores.
I added this link on edit.
http://www.batterystuff.com/tutorial_battery.html#3
I have two Sunlyte 12-5000 Photovoltaic 100AH batteries. They are designed for low amperage charging from a solar array although they will take a regular charge from the truck/RV charging system or a regualr plug-in charger without damage. The spec sheet gives you an idea of why it is so important to keep the batteries topped-up. For these batteries maintaining the charge at no less han 80% of full charge means 2-3 times the life expectency. My friend has one of these in his truck and it is still going strong after 10 years.
http://www.tpscrail.com/Products/GNB...0datasheet.pdf