Battery dry cells question

[Ed]

I have four batteries on a 426. Two 4D's in the house bank, a 12 volt deep cycle as a start battery (I know that should be a cranking battery - but I didn't install it) and a 12 volt for my bow thruster. I have an oversize aulternator - but is a "smart one" an inverter charger and a gen set. the boat was just delivered to SC from CT. It was plugged into dock power for a few weeks prior to arriving. I just checked the battery level - the boat has been on shore power here for about a week just now getting to the systems.This is what I found. One 4d the water level OK, the start battery OK - a little low but above the plates. Haven't checked the thruster battery a two person job due to location. The other 4d is the problem it was below the plates - significantly below on 4 of the 6 cells. The two pairs at either end of the battery, the two cells in the middle were full.Any ideas what is up? Havent had any problem for the two months I lived aboard the only difference I see is that the boat was motored about 125 hours over about 10 days and the gen set was run for 50 hours.Don't understand why one battery cooked and the other didn't. Any insites/ guesses/tests I should do would be appreciated.Thanks Ed

 

[Bill Bell]

You have One Bad 4D

The 4D battery that had 4 dry cells and 2 wet ones probably has 2 dead cells, the wet ones. Probably your alternator was putting 14 volts into a battery that only needed 8 or 10 due to the shorted cells.I've had that problem on a trip to the Bahamas last spring. I disconnected the bad battery until I could replace it and my charging went much better. The bad battery was only a couple of months old.You probably are charging 30 to 40 amps long after the batteries should be charged. If you check the voltage of the house batteries, you probably won't see 12.6 volts when they should be fully charged.Bill

 

[Debra B]

4d lost cell after 3 months

The last 4D I had - house brand from one of the big marine center chains - lost 1 cell after 3 months.Thats when I switched to Trojan Batteries and to golf carts. The 4D was too heavy to move anyway.

 

[Debra B]

length of battery cables matters if parallel.

My friends in the solar power community tell me that lenght of run does matter in batteries that are in parallel (as in your house bank). Having one set of leads shorter that the other will skew the load on the battery to the one with the short cable. This is worse if the cables are undersized and present a high resistance.Don't wire one battery to the charger and then wire the next battery to the 1st. Wire both batteries to a pos. and neg. terminal and then connect to the house system, charger, etc.In practice, this can also be impacted by corrosion of the terminals. Corrosion is an insulator and will also cause one battery to get most of the load.