My Battery Keeps Fizzing

[antoche]

I have an 8D wet cell battery (~220Ah) from 2004 as a house battery. The boat is most often in its marina berth, with a 5-step shore-powered charger on the battery. I am a liveaboard, using the battery constantly.

After I last topped up the battery, the charger (which was usually in float mode) keeps being in absorption mode, and the battery immediately gases and loses a lot of water. The specific gravity never indicates more than 50%-75% full, and if I stop the charger, the battery goes down to 10.5V after a day.

It seems obvious to me that the battery is dead (and not prematurely), but I'm puzzled about its behaviour. I thought that a dead battery simply had close to none capacity? I.e., I would expect it to charge very quickly and discharge in the same manner. In my case, it looks as if the battery cannot be charged at all.

Does this indicate something specific about the way the battery died? Is there maybe something wrong in the way I handled it?

I am now on the search for a new battery, and I'm hesitating. AGMs and gel seem to have more capacity for the same size (up to 260Ah for an 8D apparently), and 200Ah is a bare minimum for my usage. On the other hand, I would have to change my regulator, and it sounds like these types don't like being kept close to gassing charging regimens. Plus, it's difficult knowing which brands are the good ones here in New Zealand, as the choice is different from what's available in the US and Europe. I can see Ritar, Odyssey, Vision, Amp-Tech, Prolite... Trojans and Optima are available but not in the capacity I need, apparently.

Any recommendation?

Cheers,
A.

[colemj]

Sounds like you have a shorted cell in the battery. That would keep it from reaching float voltage, so your charger would keep trying to charge it - overcharging the other cells in the process. When at rest, you would only measure voltage across 5 of the 6 cells, which is 10.5V

Mark

[David M]

6 years of life for a standard lead-acid is pretty decent. There is nothing odd about it no longer holding a charge.

You will pay a lot more money going from a 200 amp-hour to a 250 amp-hour battery. Plus doing whatever is necessary to change out your charger with one that has a gel cell setting or an AGM setting, if your charger does not already have that setting.

You have to decide if it is worth all that fuss and expense over an extra roughly 50 amp-hours of storage capacity. The other alternative is to add another 8-D battery saving you the fuss and doubling your existing capacity. You could also add a smaller 4-D or Group 27 battery if you want additional capacity.

[senormechanico]

I agree with the above.
Colemj has nailed it, shorted cell.

[btrayfors]

Don't be fooled by the battery ratings.

Example: 8D flooded batteries (not AGMs or Gels) come in various ratings from about 220AH to as much as 275AH. Rolls, for example, has an 8D rated at 220AH and another at 275AH. Other brands are available generally in the range from 225 to 255AH.

You're right to be concerned about both price and complexity of switching to AGMs or gels. Since price seems to be a major concern, I'd stick with flooded batteries.

If you really need more capacity, you might think about different battery sizes. For example, 6V golf-cart batteries often are the best price-point for robust deep-cycle batteries. If you could squeeze in 4 of them, you could double your AH capacity to about 450AH, and four golf carts don't take up all that much room (typical 10 3/8H" x 7 1/8W" x 11 3/16L each).

Also, at about 62lbs they're much easier to lift, and are less likely to cause a major back injury.

Bill

[David M]

My point is that the more expensive 8D's are out of proportionately more expensive with respect to their capacity to the less expensive 8D's. This does not make the more expensive ones necessarily a bad deal if you need the extra capacity per battery or you need a more durable or reliable battery.

[antoche]

Thanks everyone for the diagnostics and tips. I just realized that I can easily fit a couple of 6V batteries in place of the 8D, so I'm now eyeing towards the Trojan 6V like the T105 and T145. It seems the best option: more capacity than the available 8D wet cells, cheaper than non-wet cells, and not requiring any changes to my charging hardware.