Test battery life

[Jack Long]

I was given two "nice looking" 100amp hour enclosed (no water filling) batteries that are alledged to be "only a couple years old and still good". How can I test to see what kind of life expectancy they have left?

[David M]

Jack,
You can use a battery tester similar to this one. Auto supply stores sell them or perhaps you can find someone who will loan you one?




http://www.northerntool.com/webapp/w...3303_200323303

[Jack Long]

I could probably just lug them in...

So that will give me a sense of how many deep cycles are left? The picture doesn't get big enough to tell what those readings indicate.

Thank you!

[David M]

Battery testers tell you how much of a charge a battery can hold. I don't know if your batteries are deep cycle batteries or not. I don't think that testers can measure how many cycles are left because batteries basically go from good to bad gradually meaning they hold less of a charge with each deep cycle in addition to losing their ability to hold a charge over time.

I was just thinking that if you hauled them into a car repair garage that they could put your batteries on their tester and tell you...and not charge you an arm and a leg. You will though need to charge them up overnight on a slow charge beforehand.

[hellosailor]

100 amp hour, sounds like Group31 or similar. But "sealed" doesn't say much, are they gel batteries? "Sealed valve regulated" meaning "AGM" batteries? Or just "maintenance free sealed" wet acid batteries?

If they are wet acid, you might want to put an equalizing charge on them first, to recover any lost capacity. AGM and gel generally don't get equalized, but a thorough charging would be in order.

You can do some load testing right on the boat by using some simple loads and clocking them, i.e. put a standard 65-watt auto headlight on a battery, that's about a 5-amp load, see if it can run for ten hours without getting very dim compared to the other (fully charged) battery. The load tester from the auto supply store may be designed to test SLI batteries under heavy starting loads--that's still a good test, but results will vary a bit for SLI versus deep cycle draws.

[fcsob]

The battery tester shown above is not the way to test then. Not only do you need to load test them,after a proper charging,but the resistance should be measured And not with an ohm meter. A good quality tester will do both. There not cheap but you get what you pay for.

[AnchorageGuy]

Originally Posted by fcsob

The battery tester shown above is not the way to test then. Not only do you need to load test them,after a proper charging,but the resistance should be measured And not with an ohm meter. A good quality tester will do both. There not cheap but you get what you pay for.

Well I have used that type of tester for years to give me an indication of the state of a battery with much success. But then I am experienced in using the equipment. The battery does need to be fully charged and then sit for a period of time with no load before testing. Any test equipment has certain parameters to be useful. You can take them to a battery shop and for a nominal fee they will fully charge them and test them for you. It is still less than buying the test equipment and someone more knowledgeable can give you a definitive answer.

[hanschristian38]

West Marine stores have a tester and will test them for you. That's how they determine if a battery is not working properly for warrantee.

[David M]

Originally Posted by fcsob

The battery tester shown above is not the way to test then. Not only do you need to load test them,after a proper charging,but the resistance should be measured And not with an ohm meter. A good quality tester will do both. There not cheap but you get what you pay for.

That type of tester does load test them. There is a large resistor that heats up during the test. I agree, they do need to be load tested.

[fcsob]

David
That tester only test @125 amp draw. You need to be able to adjust the load for different size batteries to diagnose them. The resistance is to show you if the battery can take a proper charge. We use a Snap-on MicroVat among others.

[David M]

His batteries are 100 amp-hr batteries. The tester is rated for batteries for 125 amps. Thats not good enough? What is?

He isn't testing a couple of 8-D's

[AnchorageGuy]

it should not matter. The tester is designed to put a load on the battery and once the load is removed to determine the state at that point. Once you have this information you can then do further testing. If the battery bounces right back then it is probably good. The load is only applied for about 10 seconds.

[fcsob]

You are only to test a battery @ half it cold cranking capacity, not amp hour capacity. You should also test it three times with a pause of aprox 20 to 30 seconds between test.