Reviving "Dead" Batteries

Michael T

I'll try to find the article but a very boat savvy friend of mine said he had read that many deep cycle marine batteries are thrown away unnecessarily. He said he read an article regarding deep cycle batteries and particularly AGM and Gel batteries that when discharged past a certain point "appear" dead to the charger - the charger might as well be hooked-up to a brick!  BUT, in reality the "dead" battery can be brought back to full charge and live on a lot longer. If I understood him correctly he said the trick (and I think the Optima Battery Company released this "trade" secret) was to connect the "dead" battery to a battery having a good charge. Connect them in parallel, then connect a battery charger to them (probably to the "dead" battery). The "dead" battery will accept some of the good battery's charge but the REAL trick is that the battery charger is fooled into recognizing the "dead" battery as chargeable and it will begin to charge. Allegedly, after about an hour the "dead" battery will have picked-up enough voltage to be "recognized" as a viable battery by the charger and the good battery can be disconnected allowing the charger to be left on the "dead" battery. My friend said some of the new chargers have PCBs that recognize a battery even if it is drained to 4 volts and will charge or at least attempt to charge the battery. Interesting?

[Deleted User]

Assuming this is true Michael, I might have just traded in a salvageable 5 year old AGM for a lousy core charge on a new battery. On the other hand a new battery is always better than a five year old battery for peace of mind. I'm interested in hearing from anyone who's got first hand knowledge in this area.

Andy

Michael T

Andy, if you got five years from a marine battery imo you did well. I have seen piles of batteries, some only 3 years old stacked for removal at marinas in the spring during commissioning. I bet some of them are salvageable.

[Deleted User]

@Michael, depending on old batteries may be analogous to owning worn or retreaded tires, yes they might "work." I sure wouldn't trust them on any of my vehicles. Likewise with "factory reconditioned" anything. Penny wise, pound foolish as they say.

Andy

Michael T

@andy - if you're going to look at AGFMs again take a look at the "thin plate" AGMs. The prices have really come down and they have beyond amazing specs: like 400 discharges to 80% depleted, charging rates at 300% charge acceptance rates. Have a look, even if just for fun. I know North Star makes them. I saw a trawler on out latest voyage who has 4 Northstar series 31 thin plate AGMs properly wired  in  parallel and he says he can run two fridges, his head, lights and some other devices for 3 days with no charging, 5 days with a one day charge (at idle) for about an hour and 7 days with a charge (at idle) of 2 to 3 hours. That's really awesome. That's freedom.

Dream_Inn

MT, that really does sound amazing!  I'd love to go for our 3-4 day weekends and not have to worry about charging!  & then when I do, it is only a couple hours once.  I'm on my 4th season with the batteries, so I probably have one more left, so I'll be looking.

Michael T

DI the guy using the AGMs  was an American guy from Florida who had brought his boat up the American inland waterway and was completing a couple of "loops" through Canada. He was returning to Florida this week back down your inland waterway. He seemed to really know boating and swore by the thin plate AGMs that he had purchased before beginning the trip.