I reconditioned a very good new battery that started to die, then got the best unit I could find (with in reason)and leave it plugged in all the time. --->Batterytender model 2012 for AGM only, about 85$
May I suggest to the OP to have his battery go to person to read up on Deltran, tech section, and read up on the smart tenders they produce. Then goggle east Penn and read up on the information concerning "Gel" type batteries and the AGM batteries. Good reading and informative.