Next time, get 2 6 volt golf cart batteries from Costco or Sam's Club and wire them in series. Same price as 12 volts, but, with maintanence, will last much longer. You can get the battery watering kits that will let you keep them full with a couple pumps on a squeeze bulb so you never have to open the caps. The golf cart batteries are the most bang for the buck and are true deep cycle, unlike a lot of the RV/boat batteries out there. If they will be "unattended" for 3 months, just fully charge and do not put a trickle charger on them. Last thing you want to happen is for them to boil dry over 3 months. Sitting unused for that length of time is tough on any battery but that will make the best of it.