testing deep cycle battery AH

Hello Everyone From Northeast Mississippi, Glad to be here, great looking forum....I need some help please, I have a opportunity to purchase some used deep cycle batts that are a change out from tornado alarm systems (sirens) I have no idea about age or anything else about them until I go to look at them, they are at a wholesale/junk dealer's place that he purchased somehow. My biggest question is does anyone know how to test/check the AH life left in them? There are several and I only need a couple for my small system I am making (I assume) so I thought if I could check them and pick out the best two would be to my advantage. Any comments/instructions/ on the best way or a cheap tester to check AH would be greatly appreciated, also any suggestions on what and how would be the best way to test these period. Thanks in advance for your help.

Glenn Stanford

Most places such as alarm systems, phone companies, etc. generally swap out their batteries long before they need it. These are emergency backup units that must be reliable.

I know a guy who has bought these backups several times. He has had great luck with them.

Thanks for the encouragement and reply John...

Your best bet is to take a voltmeter with you and check what voltage the battery is. Then charge the battery fully. After the battery is fully charged, place a good load on it like a headlight bulb for approximately one minute. Let the battery rest for one minute and then check the specific gravity of each cell in each battery your looking to buy. The best battery will be the ones whose cells specific gravity are very close to the same with very little deviation.

Thanks for the reply Eric, Problem is these are all on a pallet and at a business I will not be able to take the time to do a test of this nature, Therefore I need a quick method of evaluating these batt conditions, that is why I am searching for a tester that does not require history to ascertain condition of each batt. Thanks for your help.

If unable to perform this test your best bet is to check the current water levels and specific gravity, again finding the ones with the least deviation between cells and the most water, then when you bring them home, top off the water and perform an equalization charge if your charge controller permits.

It's no guarantee, but if these were all ripped out of the same system, or multiple matching systems, at pretty much the same time... simply checking the current voltage in each cell may provide some minimal basis for comparison.

Eric's suggestion is a better test, if you have the option to test specific gravity and check water levels, do so! You might be surprised what the business will let you do if you make it clear you want to buy some.

Thanks Guys, I am hoping that the batts are unsealed to check fluid level and SG, although I need to "upgrade" my SG tester's to temp compensating type (any recommendation's) I will take along my Fluke DMM and digital thermometer and torpedo level, From my understanding he gets these batts 3-4 times a year and sells out quickly to boaters ect. So I may not have as many to choose from, I just want to be best prepared to evaul. them the best I can do, I will try to group by manuf, make, model, AH rating, ect. then preform test that I know how to do. I was thinking there maybe a quick way to check capacity, but as my luck usually goes there is no such way or animal....

Dillon, How does one check voltage in each cell? I know how to check SG but not voltage in each cell. Thanks

Oops, I meant simply each battery; mis-typed. I don't know of any practical way to get at the individual cells in a lead-acid deep cycle.

If he gets them a few times per year finding a way to be there promptly on delivery of a new batch might be worthwhile...