A few thoughts:

When you are connected to shore power with a properly working battery charger, any DC loads you have are effectively being supplied directly by the battery charger. The batteries are not really involved. I can explain in detail, if needed.

Your batteries should not experience significant water loss unless they are being overcharged. You need to have a good battery charger capable of sending the battery condition and regulating the charging voltage appropriately.

I presume you have one run of wire from the refrigerator switch on the panel to the refer compressor. Depending upon where you tap off an additional wire for a separate device, you could be experiencing a larger voltage drop in the wiring, which can be very bad for your operation and compressor.

Hi, Tony.

You are welcome. Here is more detail.

Your shore power charger wire runs to the battery bank and applies voltage to the battery bank and ALL the wiring connected to it. Imagine your battery bank is fully charged. When you turn on the fridge load, simultaneously the battery will start to provide current, AND the charger will sense that the load has decreased the voltage, so it will turn on and raise the voltage again. That voltage/current supplied by the charger will power the fridge and the already fully charged batteries will sit there with no real change.

If you lost shore power for 30 minutes, the batteries take over all the load and slowly discharge (not very much in 30 minutes). When the shore power is restored, the battery charger will supply whatever the fridge needs, plus enough to recharge the batteries.

I am not a battery expert, but I believe overcharging (too much voltage for too long) is the chief reason for excessive water loss. If you are sure you have high losses, you need to check the voltage the charger uses for the Bulk, Absorption, and Float phases of charging.

It would be helpful to know specifically what battery charger you have. You only mentioned "very good..with ammeter...". Losing water from your batteries is a symptom of inefficient, at best, charging.

Tony, WADR, sometimes the little black box may be better than the older hunkin' box. :):):)

The reason i asked is that older boats came with what are now very questionable chargers.

So, yes, it would be helpful if you could let us know what make and model it is, and a picture may even help, too.

Pretty basic unit, I just read their docs from their website which says it goes into bulk charge at 14.5 volts for 4 hours then into float at 13.6 for flooded lead acid. That's not the way a really good charger does it. There are no adjustments. Almost sounds like a ferroresonant unit with a timer but maybe not. At any rate, appears to not be a high end unit. A timed 4 hour bulk charge at 14.5 volts on a battery bank that does not need it will definitely increase water consumption.

I agree with Bud that the charger is definitely not a high-end unit. Can't say it is your problem, but I had a charger fail on me and it was cooking the batteries by severe overcharging. The only way to tell (that i know of) is to measure the voltage it is applying at various stages of the charging cycle.

An expert would advise you better, but I would try this: Check that your electrolyte level is good. Disable the charger then discharge the battery bank a bit so that the resting voltage is perhaps 12.5 or so. Then turn on the charger and measure and record the voltage with a multimeter. Take measurements every 15 minutes and see how it behaves until the voltage stabilizes at the float value (factory set for 13.6V).

If it takes hours and doesn't seem to ever drop to 13.6V or so, then it "may" be overcharging. BTW, the capacity of your battery bank plays a role in the time involved with a larger bank taking longer to recharge, especially with a small 20A charger.

Tony,

Bud and Duane have identified the major potential issues with your charger. Since you have an older boat, there's no way for us to tell when that charger was installed. In most, but certainly not all cases, the presence of an ammeter on a charger means it's pretty old, and perhaps built before true three stage charging (plus equalization) came into being based on proper battery charging regimens promoted by the Ample Power Company in Seattle in the later 80s.

Over the course of many years discussing chargers, we identified some that were questionable, Charles being among them, ProMariner FLYBACKS being the other (NOT the [B]new [/B]ProMariners which are identical to the Sterling Ultra Pros).

You might be interested in this 2002 discussion, starting with Reply #12.

[url]http://c34.org/bbs/index.php/topic,605.0.html[/url]

Good luck, if it was my boat, I'd take Bud and Duane's suggestions and start doing some voltage and time measurements to determine how the charger works, after you identify if it is one of the questionable older models.

PS - added 8/17: please recognize that this link was written in 2002, with a 2005 followup. The Xantrex chargers available back then were superb. NOT ANYMORE. Please, stay away from Xantrex equipment. Maine Sail has written an excellent battery charger How To: [url]http://forums.catalina.sailboatowners.com/showthread.php?t=125606[/url] It includes recommendations for brands of new chargers that he suggests are quality and fairly priced.