Battery Maintenace

[boto]

We have three 31 wet cell batteries on board. One dedicated to the engine with the other two running parallel as a house bank. I plan to change this setup to a series as well as add a fourth battery. The question is that recently we had been awawy from the boat for a couple of weeks, when we returned and I checked the levels on the batteries I found that three of the cells of the "first" house battery had been depleted of water (we had left the hot water tank on). I topped off the batteries and everything appears to be ok. However, the house battery that had been depleted is hot to the touch, it seems to be taking a charge, but the heat has me concerned. Is there cause to be concerned?

On another note, am I'm sure there are other threads on the subject that I haven't gotten to yet, any suggestions on setting up the batteries in a series? I believe what is happening is that the "first" battery is being run down by the "second" and is constantly being charged by the charger.

Thanks

[camaraderie]

If you wire 12V batteries in series you will get 24 volts. Are you sure that is what you wish to do?
Do you mean you wish to divide the batteries into 2 banks...one with a starter battery and one with 3 group31's in PARALLEL to increase your house bank to around 300 amp hours at 12V?? Or are you going to 6V batteries wired in series pairs and then parallel?
Some diagrams here: How Lead Acid Batteries Work

On your other question...exposed plates are NEVER good and if the batteries are not dead...you have greatly shortened their life. How many amps is your charger? Should be around 20-40 for your existing bank of 2 G31's. Is it a 3 stage charger? When you remove ALL charging AND all loads from the batteries and wait a few hours...then take voltage readings of the individual batteries ...you should still see at least 12.6V on all of them. Better yet...get a hygrometer and measure the specific gravity at each wet cell after charging and waiting some hours. If one battery cell is damaged...it can ruin the others...and everything else in the bank.

Something like this setup is what I would suggest for your setup assuming you will be sticking with 12V batteries. Note that the battery in position #1 would be the starter and the battery in position #2 represents any number of paralled 12V deep cycle batteries.

[boto]

camaraderie,

Thanks, yes I had the lingo wrong, looks like we want to continue in a parallel system, Im just concerned that the batteries later in the series are drawing down those in front.

I plan to shut everything down and am picking up a hydrometer this evening.

Thanks for the link, will check it out.

[GordMay]

I don’t recommend the parallel connections Von Ventzel pictures, wherein the load is connected to the positive & negative of the same battery.
Rather connect the loads (and charging inputs, pictured below as 'Inverter') to the positive of one battery, and the negative of another.

Series Parallel (left) & Parallel Connections (right):

[AnchorageGuy]

31s seem awfully small for a house bank on a boat of your size.

[boto]

Chuck,

on the size of the batteries, I see that you too are on a 40, what size batteries due ou recommend?

[S/V Illusion]

If I may, the size of the boat (LWL) or any other measure of length is totally irelevent with respect to battary bank size.
The only considerations when sizing a battery bank are:
1. electrical demand expected
2. charging capability and ratings of charging source(s), and
3. your individual maintenance habits.

The bank should be sized based on an energy analysis of your electrical demands, e.g., if you expect to use 50 amps between recharges, you don't need a 600 amp bank (although bigger than needed isn't necessarily a bad thing as long as you consider #2 above).

Your charging system should be rated and capable of properly recharging in a reasonable time, e.g., that 600 amp bank half dicharged will take forever to fully recharge with a 50 amp alternator running at idle on the hook.

Lastly, if you tend to never chaeck the batteries, you might want to consider gel or AGM batteries, again depending on whether your charging system is appropriately modifiable.

In other words, size your batteries based on what you need rather than how many the boat sleeps...

Originally Posted by boto

The question is that recently we had been awawy from the boat for a couple of weeks, when we returned and I checked the levels on the batteries I found that three of the cells of the "first" house battery had been depleted of water (we had left the hot water tank on).

Your batteries are powering your hot water heater?!? That should never be! A typical hot water heater uses over 1000 watts and will drain the biggest battery banks in hours. And you battery bank is very, very far from the biggest around.

I topped off the batteries and everything appears to be ok. However, the house battery that had been depleted is hot to the touch, it seems to be taking a charge, but the heat has me concerned. Is there cause to be concerned?

It sounds like you have a shorted cell. That would be consistant with allowing the water to run down below the levels of the plates, it might have even been the CAUSE of the water disappearing. Check the specific gravity of the individual cells in the battery if they are different, the battery is toast.

[RaptorDance]

I don't think anyone mentioned your likely problem:

You're charger overcharging your batteries and boiling off the water! (I'm guessing your charger was left on)

What charger do you have? Is is a recent model "smart" 3 or 4 stage charger?

I suggest you look into a good battery monitor (like a Link 10) to keep an eye on things.

FWIW we have 6 Group 31 East Penn Gels in Parallel. Monitored closely... They've work fine for years.

[boto]

We have three 12V 750CCA Deep Cycle batteries, Nautilus NG-31 with a 12V30A Samlex smart charger. We had a similiar problem when we first purchsed the boat, the batteries were five years old and the old charger was boiling them off as it would never shut down, so we replaced the batteries and the charger, all new in '06. As this was an expensive replacement we plan to follow up with the folks that did the install for us.

Any thoughts on this equipment is welcomed.

Also, moving forward, we want to expand the house bank with another 31, given space considerations we are considering a smaller starter battery. any suggestions?

[Rick]

Pay particular attention to Gord's diagrams above to ensure good source and load sharing of each battery and to avoid degradation of any one battery.

Look up the kW rating of your starter motor, divide by 5 and find a start battery having that number of CCA rating or higher. An optima battery having that number or higher will probably be the smallest volume reliable start battery for your engine. It will give you higher voltage under start load than a flooded-cell battery and will tolerate 15 Volts.

The only thing "wrong" with the Samlex charger is that they rate the acceptance voltage only to 14.3V which is at least 0.1 V too low for proper capacity recovery in the vicinity of 25 deg C. Hopefully you can get around this by using an alternator externally regulated with a unit that allows you to set the acceptace voltage higher than 14.3V and thereby properly recovering a deep discharg cycle.