Re: Stus-List Drained AGM battery

[Bill Bina]

AGM batteries are available as deep cycle batteries, as capable, or more capable than any flooded or gel cell deep cycle battery. The reason all AGM batteries are okay as starting batteries is because AGM batteries have inherently low internal resistance, which allows them to deliver higher amperage for short periods when it is needed. A flooded Deep Cycle battery has higher internal resistance and cannot deliver the higher amperage (cold cranking amps) needed for use as a starting battery.  AGM's deep cycle as well, and as long or longer, than any flooded deep cell battery. Just like a flooded deep cycle battery, they should not be cycled lower than 50%. Some advertising copy for deep cycle AGM batteries is a little misleading, and claims that the battery is "specially designed to also be used as a starting battery". This is bunk as far as the name brand AGM's. Their ability to be used as a starting battery is due to the fact that AGM's all have this ability due to talent they are born with. Just the same, an AGM that is going to be used as a starting battery should be upsized to the next size if there is room, because for a given size they do not deliver quite as many cold cranking amps as a "real" starting battery that has thinner plates. Some retailers, such as Walmart DO sell some batteries that they claim are dual purpose starting/deep cycle batteries. These are not true deep cycle batteries, and if used for deep cycle applications, will not last very long.  Stick to Lifeline, Trojan, or similar brands and you will get a true deep cycle AGM when you ask for one. Any battery that has been run flat should be considered a candidate for replacement, regardless of being AGM, Gel or Flooded. It's useful life has been shortened, even if it otherwise seems "okay". If it is in a non-critical application, you can try to get another year or two out of it, but I wouldn't go across an ocean with it, even if I had to pay full price to replace it. Bill Bina On 8/27/2013 10:59 PM, Rick Brass wrote: Chuck;   Whether he is on a mooring is sort of immaterial. David already indicated that the engine alternator had no effect on the dead battery during extended period (3 or 4 hours IIRC) of running. Below he says he used a common trick to show enough battery voltage for his smart charger to turn on and has managed to get the dead battery charged up to 10 volts after several hours on charge.   I agree with your suggestion to get the battery charged up and let it rest to see if it will actually hold a charge. Others have suggested that the battery be load tested after charging, which is also a very good idea – and something just about any auto parts store will do at no cost.   I personally think the battery is a good candidate for warranty replacement, unless David is very lucky. AGM batteries are designed to be automotive starting batteries – designed to be at 85-90% state of charge or higher at all times. They don’t last long in deep cycle use. If you run one of them dead, it is really hard to get them to ever come back.     Rick Brass Washington, NC

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