Battery maintenenance when away for long periods

[cardminger]

Hey all,


Wondering what you cruisers do for battery maintenance when away for longer periods of time (4-7 months).



A little more info on the situation -


The boat lives in the water, in the marina, plugged into shore power.


We run 6 Trojan water filled batteries and one AGM engine start battery. The battery banks are isolated by an ACR and hooked up to a Xantrex multi-bank charger.



I know it is bad to let the Trojan batteries run until they are "dry" but sometimes it is hard to find someone reliable to fill them on a regular basis.


If it matters, the boat is in Central America so the climate is hot, hot, hot, mixed with damp!


Thanks in advance for the advice!

[waxy]

How often do you normally need to water your batteries while connected to shore power? We recently had to leave our boat for nearly a year in a marina, connected to shore power. We had all necessary 12V breakers off so the battery charger was pretty much in trickle the entire time. When we came back to check the batteries (which I was pretty sure they'd be toast) the water level had barely dropped from where we left them. We have 8 6v batteries from costco about 2 years old.

[Stu Jackson]

Have you considered a small solar panel and controller? Disconnect from shorepower.

[a64pilot]

No, stay connected, I’d run a small AC set pretty warm just as a dehumidifier.
However I’d set my chargers to the min. acceptable float voltage, water usage should be almost zero then.

[Locquatious]

If you are in the tropics, charging your wet cell batteries above 13.2-13.3V will cause them to develop gas bubbles and eventually dry out. We set our solar panels to charge no more than 13.2V and have always returned to wet batteries. If your solar controller allows this voltage adjustment, use that. If your solar controller only allows higher voltages, consider blocking some of the cells on the panel so that the maximum voltage the panel can produce is 13.2V.

If you leave the boat plugged in and on a battery charger, move the charger sense wire to the AGM starter battery. This will cause the charger to just control battery charging for the AGM which can be stored at float (say 13.6-7V) and would not be hurt by periodic full voltage charging. Full charging would occur after power outages or if the boat is momentarily unplugged. If you have an isolator, connect the charger to the isolator and feed the wet cell batteries through the isolator. The isolator will drop the battery charging voltage by around 0.7V. If you don't have an isolator, charge the wet cell batteries and then insert a Schottky rectifier diode in the positive wire between the charger and the wet cell battery positive post. This will drop the battery charging voltage by around 0.4-0.5V. Try a https://www.digikey.com/product-deta...LGOS-ND/918594 rectifier diode. This will allow 25A of current during power restored charging. You can probably use 10 ga wire connected to the charger cord, crimped to the rectifier pin (right pin looking with tab down), and then another wire connected to the other pin or tab with the hole. Ideally the tab would be connected to the battery terminal so the rectifier is cooled via the terminal. Make sure you keep the connections insulated and don't let the rectifier tab touch another conductive surface other than the battery positive.

[MJH]

#1. All batteries should be of the same chemistry when being charged by the same source...yours are not.

#2. How long is your boat going to be out of reach? If you can't find someone reliable to keep up the battery water levels then you need to change to a battery chemistry that doesn't need that level of care like AGM or GEL. My 8D Gel batteries are 14 years old and require no maintenance.

Good Luck.

~ ~ _/) ~ ~ MJH

[roland stockham]

For periods of up to 6 months this should be no problem. To be safe you could overfill with water to give the max reserve but 6v deep cycle batteries should have plenty to last. Would be worth setting the charger at min float level. The one thing you do want is for someone reliable to do weekly check, all sorts of things can go wrong so you need someone experienced to walk through the boat, check battery voltages etc. It is worth paying top dollor for this and can save a fortune if something does go wrong. If she is in a marina talk to the manager.

[john61ct]

Better to isolate completely, and then connect to recharge overnight every 2-3 weeks.

Letting them run dry is murder.

The cost and difficulty of finding a reliable caretaker needs to be weighed against drastically shortened bank lifespan.

[Compass790]

I agree with the others who say lower float voltages. We are storing 225 Amp Crown 6v deep cycles in pairs at 13.3v float & they use virtually no water & they are old batteries but it isn't as hot as your situation

[a64pilot]

Being hot further reduces the charge voltage required.
Just me, but I’d bet even 13 B isn’t too low, as long as nothing is drawing from them

[transmitterdan]

You can get automatic watering systems for flooded batteries.

But if the float voltage is correct and temperature compensated you should not have to add water except maybe once a year when on float. Water is mainly lost during heavy charging. It should not be lost whilst on float.

[KP44]

The charger voltage is set too high if it boils the water out of your batteries. Check the voltage and adjust it lower.
There are also special caps available that condense the water and return it to the batteries. Those might help. The special caps are very tall and might not fit in your battery box.
I used 8 Trojan 6v batteries and they lasted 10 years.