Can You Test for a Bad Cell in a Battery?

[Pat Anderson]

OK, Wally World replaced the big Maxx 29 deep cycle marine battery in mid-July. This battery charges up to 12.5 or whatever, but it drops overnight to 12.1 with virtually no load except the 80 milliamp fan on the Airhead. Don't run the fridge any more when the engine is not running. Not a satisfactory situation at all...so, is there some way to test this sucker to see if it has a bad cell or something?

[BrentB]

yes take back to Walmart and request a battery load test or if
you have a battery hydrometer, test each cell. even the cheapie ones with the floating balls works well enough to detect a bad or dead cells
I purchased load tester (carbon pile) from Harbor Freight and used a 20% off coupon from the ad and also received a free LED flashlight with batteries. It made my day

[Sea Wolf]

Pat-

Brent's right, of course, let Wall Mart test it for a bad cell, or whatever.

A 80 milliamp draw over 10 hours is only 0.8 amp-hours, not enough to register much of any voltage drop on a 100+ amp-hr battery.

The only other possibility is that you have some other draw you haven't considered, or you're not aware of, such as an anchor light ( max. 1 amp x 10 hours = 10 amp hours), still not much of a drop (should be 12.6v).

See 95 Battery Condition and State of Charge Charts

So, unless you have a big unknown drain, the battery is faulty, and which cell or cells are bad is pretty much moot, but they can test it for a bad cells(s), and also see if it will hold a charge overnight independent of any small load.

Good Luck!

Joe.

[Matt Gurnsey]

Which boat is this on, and what is the engine? Are we sure the battery is being fully charged by the engine, and not just showing a surface charge?

Just wondering, because if this is a second "bad" battery, my mind asks if there is a: poor workmanship on the battry line, or b: something not quite right with the charging system.

[starcrafttom]

pat if you are coming by this weekend on the way to the crab shack I have a load tester you can use.

[Alyssa Jean]

Matt this is on his 25 and he has a Honda 150 on it. He did replace his charger a few months ago. Heck, he will chime in here shortly.

[Pat Anderson]

Yes, it is the house battery on the CD25. The starting battery and the house battery both have the same charging setup, engine with voltage sensing relay when we are out running and a 20 amp Guest in the driveway. The starting battery is just fine. The Guest shows that the house battery is fully charged in the driveway. I may pick up a cheapie hydrometer and check the cells. I also might just turn everything off and put my multimeter in ammeter mode into the circuit to see if current is flowing that I am not aware of. It is such a pain to pull the battery and take it back to Walmart, I could take it down to the Model Garage in Fall City (a good, old-fashioned repair shop) and have them load test it I imagine.

[T.R. Bauer]

Depending on where you are at, and how buried the battery is, you have already spent more time posting mesages than it takes to check the cells with a hydrometer. I think you were alluding to that too But with that said, I bought a costco battery (same maker as Walmart, Johnson Control Group), put it in the boat last year as I wanted a nice new fresh battery, and guess what, dead cell right off the shelf. So, it does happen and Johnson Control Group makes fine batteries in general. However, a battery with a dead cell and the surface charge removed should not read 12.6 volts. It should read about 10.5. Being that this is the second battery in just a month, something isn't right, I'd check everything, especially those pesky connections.