I have a house bank of 4 vented batteries with a NewMar shore charger (20 years old). The batteries are getting on in years (although they have not been cycled much as I mostly day sail) and I had them tested (and topped off) this last April. They came out marginal, but I thought I could get through this year with them as I am not cruising. I am doing something on the boat everyday (as it is at the dock at my house) and this afternoon I got a surprise of a nasty smell when I opened the boat up. I first suspected the head, but it was not that; when I went to turn on the battery switch I noticed that the battery compartment (under the aft quarter berth) was especially warm (it has been in the 90's here and with the boat closed for T-storms it does get warm). I immediately disconnected the shore charger and investigated further. There was a hissing/humming sound coming from one of the batteries; it was boiling off fluid! I disconnected all the batteries and removed them from the boat. The hissing battery (#4) has one cell that looks to be dry and even disconnected it is still hot. Battery #3 also has a nearly dry cell (both read 12.8 volts still). Batteries #1 and #2 still have fluid in all cells but some are low and they read a bit higher voltage at 13.1 volts.
My question is; is this the way batteries die? Or should I suspect the shore charger? When I initially turned on the battery switch my bank meter read 13.1 volts, which is not too unusual, but I did not look at the amp load (it should have been Nil) as I wanted to turn everything off because it seemed too warm.
I have had the boat (and these batteries) for 5 years and normally I check the fluid a couple of times a year and it seemed fine. This is the first time I have noticed real boil off and I am not sure if it is due to the hot weather, leaving them on shore charge or because their time was just due.
thanks for all comments.
As soon as I finish writing this note, I will be leaving for a local golf-cart vendor's shop to exchange 4 7-1/2 year old T-105's for new. Our bank gave up the ghost in much the same manner as did yours although the first sign that things were not well with ours was the gas sniffers repeatedly going off, which I suspect was caused by the hydrogen gas and the frequency with which I had to add water to the two batteries first in line to the charger. Our charger is a Heart, controlled by a Link 1000, that provides a 3-stage charging process. Despite its age, if the NewMar follows a similar sequence, there would be no reason to replace it. If not... The "death throes" of our batteries was exactly the same as you describe. One cell cooked dry, undoubtedly due to an internal short, less than 3 days after watering the cells, last week. (The battery was so hot and distorted, I was concerned that the darned thing would catch fire.)
Our golf-cart company battery guy suggested that our batteries lasted so long because we have the 3-stage charger, religiously check the water levels weekly to ensure the plates are never exposed, and periodically "equalize" the batteries per the technical instructions on Trojan's web site whenever the hydrometer indicates much of a difference in the specific gravity of the electrolyte between the cells. The only additional measures I will take with the new batteries is to swap the order around such that the first in the charging line becomes the last every year and add the hydrocaps described by Bill, above. And, unless we're planning on using the yacht, I will not keep the charger running quite so often/long.
If you have difficulty finding affordable T-105's, Main Sail (an acknowledged expert on matters electric) recommended US Battery US-2200 XC2 batteries as an equivalent but somewhat less costly replacement. Fortunately, I found that T-105's are quite a bit less costly here in Florida ($106 each) than they are in other venues, simply because so many are sold. (By comparison, in January '06, we paid only $65 each for the batteries. Of course, since then the price of lead has quadrupled so the increase is somewhat understandable.)
N'any case, good luck with your swap out. Check your golf-cart companies for replacement batteries. They seem to be the least costly source, at least here in Florida.