Anyone know much about deep cycle marine batteries? I have two in my basement that are supposed to run the battery back up for my sump pump, but they tend to fail reliably (lol). One battery is hooked up at a time to a continual trickle charger that runs off the house electric. When the power goes off and the sump well fills, the float on the backup triggers both the backup pump running off the marine battery, and a "siren" thing that sounds like a smoke detector. I call it the "hey, the house is flooding" alarm. I can't seem to keep these batteries charged right. The charger often throws a "charge fault" error, which I'm assuming means it's doing jack for the system. Do these marine batteries have a shelf life? Max number of charges? Does keeping them hooked to the charger at all times degrade them? Any way to tell if they're beyond useful life?