Checking the charging capacity of SLA batteries

How can I check the charging capacity of the sealed lead acid batteries which I use to power my fish finder?  I have two battery boxes.  One of the batteries provides enough juice for two days of fishing.  On a recent trip, the other battery pooped out after nine hours of fishing, which brought my day to a premature close.  A salesperson at Batteries Plus told me that SLA batteries only last for 2-3 years, and they don't have a way to test the capacity of a battery, but his job is to sell batteries.  Any suggestions?  Or should I just go buy a new battery?

You could test the internal resistance of the battery to get a feel for its "health". Compare the resistance of a known healthy battery to the resistance of a questionable battery, and you can get a feel for its condition.

This isn't going to spit out a number of amp hours, but if you had the time and energy I bet you could come up with a "calibration curve" relating internal resistance to amp hours.

Or you could just buy a new battery...


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There are battery testers that handle SLA.  I'm surprised Batteries Plus didn't have one.  They aren't cheap.

-Allen

I bet you could take it to an auto parts store and have them hook it up to their battery tester.


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Fully charged it should read over 13V.  If it shows 11-12v after a full day of charging, your battery is toast.  The Norco Genius chargers on Amazon are a great deal, pick one with SLA capabilities.