How long should AGM deep cycle storage batteries last?

Posted By on December 18, 2019


Although my boating life isn’t quite this bad (thanks for the photo Fatty Goodlander), it is frustrating to be dealing with what I thought was an already “fixed” problems aboard Encore. Besides not using the boat often enough, the re-fixing of problems a second time is frustrating, time consuming and costly.

Back in 2013 (has it really been that long?) I replaced both the failing batteries and inverter/charging system with upgraded 105 amp hour DieHard batteries (got a deal)and a 2000 watts inverter, charging and monitor set-up. All seemed to be working well for the past several years, but recently noticed that the batteries were not holding a charge. A couple weeks ago while patching the bimini with new wear strips (photos below) and cleaning up the condo for our winter renters, the batteries were completely flat. Hm?

The old (left) wear strips and the new replacement strip with some reinforcement (right)

Could these expensive batteries have failed after only 5-6 years of light use? That seems fast for batteries that sit on a charger and aren’t usually cycled up and down … but nevertheless, I hauled them these weighty behemoths out of the bilge and will need to get them tested. On the other hand, perhaps 6 years is about all that deep cycle AGM batteries will last?

Personally I think I would be better isolating them and keeping them disconnected when I’m not on the boat, especially if there is a phantom electrical leak (which seems unlikely).



Desultory - des-uhl-tawr-ee, -tohr-ee

  1. lacking in consistency, constancy, or visible order, disconnected; fitful: desultory conversation.
  2. digressing from or unconnected with the main subject; random: a desultory remark.
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