6V battery charging problem...

[chachere]

I just replaced the batteries in my boat, which were 12V flooded, with a pair of 6V golf cart size batteries from WM for the house bank, wired in series. For some reason, however, only one of the 6V batteries seems to be taking on a charge from the charger, the other has stayed almost flat, as indicated both on my multimeter and as well by testing the specific gravity with a hygrometer. Obviously, since the batteries are wired in series, both must beare receiving an equal charge.
Could it be that the store failed to add battery acid before selling it (do they do this at stores)? Or is it that the battery is just n.g.? Or some other reason? Any other theories?
- Matthew

[btrayfors]

Matthew,

You're right that:

- IF the batteries are properly connected in series (positive pole to negative pole); and

- IF the connections are clean and tight; and

- IF the connecting cable is of sufficient size (I like AWG 1/0 or larger); and

- IF the electrolyte level is OK; and

- IF the charger is properly connected (to the positive pole on one battery and the negative pole on the other battery)....

....then, both batteries should be charging more or less equally.

Sometimes there's a big difference in the capacity of even new batteries, depending on how long they've been sitting without a full charge.

I'd take the offending battery back to WM for exchange, and check that the replacement battery is good before hauling it home.

Bill

[LakeSuperiorGeezer]

One battery is most likely sulfated. It is probably older than the other and self dischrged over a year's time, or maybe it went out to a customer who discharged it and brought it back to WM and then it sulfated in several months while in the discharged state.

[sidney777]

I had to take a 6v back to Sams club right after I bought it. They tested it and I got a new one. (of course the other 6v I just bought was good)

[chachere]

I went back to WM with the battery, they said that its not charging properly because its hooked up to the screw-type terminals rather than the clamp on posts. I've never heard of this before -- the other batteries charge up fine, and all my boats have always been hooked up that way. Are they pulling my leg? If this is so, why are screw-type posts referred to as marine terminals?

[hellosailor]

"its not charging properly because its hooked up to the screw-type terminals rather than the clamp on posts."
Then the screw terminals are not making proper contact inside the battery, and the battery is defective. Have it replaced. The dual-terminal type batteries can use EITHER terminal or BOTH terminals with no difference.

[Maine Sail]

Originally Posted by chachere

I went back to WM with the battery, they said that its not charging properly because its hooked up to the screw-type terminals rather than the clamp on posts. I've never heard of this before -- the other batteries charge up fine, and all my boats have always been hooked up that way. Are they pulling my leg? If this is so, why are screw-type posts referred to as marine terminals?

What they told you is complete rubbish. Both of those terminals go to the SAME spot inside the case and are one in the same..

Where and how was your charger connected in terms of negative and positive?? This is important with two batts in series and they need to be charged in series for 12V. As Bill stated above the pos lead of the charger to the pos post of the first battery and the neg lead to the neg post of the second battery. If you connect neg and pos of the charger to ONE battery it will be treated as a 6V battery not 12V.

[chachere]

Thanks -- I had never heard of such a thing, and I thought they were completely full of it. But I was given a line about "the screw terminals are only for auxiliary things, like bilge pumps, you have to connect the chargers to the posts." No technical resource I've consulted on the subject says anything like this, and I've always wired up my batteries with ring connectors on screw terminals.

Originally Posted by Maine Sail

Where and how was your charger connected in terms of negative and positive?? This is important with two batts in series and they need to be charged in series for 12V. As Bill stated above the pos lead of the charger to the pos post of the first battery and the neg lead to the neg post of the second battery.

That's exactly how I have it hooked up - in series. As I believe I mentioned in the initial post, one of the batteries charged up fine, the other didn't. Since they are in series, obviously they both are getting the same charge, so I can't imagine how the connection method -- screw terminals vs clamp on posts -- would make any difference at all.