Testing batteries

[alvitae 10+ year member]

I was told the other day that regular battery testers don't work for agm/gel sealed type batteries. Is this true? ie. Putting them on a load tester.

What is the best way to test them? I have 4 and am thinking it's time to test and see how they are doing. One is not in my car and has a fine resting voltage but when load tested it falls off fast. Maybe they are supposed to fall off fast. Get rid of energy quick and recover quick?

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[groundpound4200 5,000+ posts]

I've had big gel deep cycle batteries (group 31) fail on a digital load tester before even though they were resting at 12.8 I was told the same thing by the battery guy.