The reason for your high battery water usage is right in your post. Being at a full hookup most of the time means your converter/charger (or inverter/charger) is always charging. Typically, the charger side of particularly converter/chargers are inexpensive units that ALWAYS pump an excessively high "maintenance" charge rate into the battery, thus causing both an overcharge situation (i.e. shorter battery life) and also "boiling off" the water - the "boiling" be the chemistry of converting water to sulfuric acid by adding electricity. These inexpensive chargers simply do not have the sophistication to "correctly" charge a battery especially when left on all the time. When the battery becomes fully charged the inexpensive charger “float” charge output can still be way too high. The more expensive inverter/chargers typically have a more sophisticated charger in them creating a well regulated triple mode charging profile meaning you can typically leave these units always on.

Another possible situation is that your batteries are heavily sulfated in which case they will never seem to stop taking a charge faking out any charger to keep feeding a heavy charge and the same boiling off situation happens. Fixing sulfation might be possible thru a fancy computer controlled true three mode charger or it might be too late and the batteries will need replacing. Go to a good specialty battery/electrical shop to have this possibility checked.

Simple converter/charger solution: If you have a battery disconnect switch for the entire house, switch it OFF AFTER you plug in. Nine times out of ten this switch will disengage the battery bank from the converter/charger entirely thus stopping the charge and your converter will run the entire coach and the charger will see nothing to charge. If you can rig an ammeter in at the battery you can verify that your switch does just that and see the float charge rate when engaged.

Best of...

-- Edited by RVDude at 20:03, 2006-09-11

What RVDude said is right, but I'll add one thing.

A half gallon or a little less is not all that unusual for a 3-4 month period. I charge almost exclusivley with solar, with a high quality, temperature compensated solar controller. I doubt I run my battery charger (inverter /charger section) more than 5 times a year unless boondocking and charging off the generator. I check my water every month and probably add your half gallon over a 4 month period. I have 4 - 6 volt batteries.

Fred,

What the charger output should be will depend (geeze I sound like Howard the attorney) on what the charger is designed to do, what type battery is being charged, and on the manufacturer specs.

Warning Science Content Follows: The first of three possible charging modes is called a bulk charge mode and is at a constant amperage (i.e. push 10 amps at whatever volts is necessary to get 10 amps by ohm’s law I=E/R) and is usually the only mode for un-sophisticated chargers or the chargers we used as teenagers. These chargers can pretend to get fancy by dropping the constant amps to 1 or 2amps for what they erroneously call maintenance or trickle mode. But they are still pumping out amps and hence are why they are battery boilers (some turn off completely which is a safer option). If a charger keeps pushing an amp or two forever the battery will literally boil out all the water/acid thus “cooking” it. Essentially you keep forcing amps into the battery tank - just like forcing fuel (the amps) into your fuel tank (the battery) it's going to spit out. Think of it this way - amps is the "volume" of fuel like gallons/minute. Volts is the “pressure” at which the fuel is being delivered. It is much cheaper and easier to make a charger that outputs constant amps than constant voltage. More sophisticated chargers will enter the second of the three modes as the voltage naturally increases during the bulk mode and shifts into the first of two possible constant voltage modes. The first constant voltage mode is designed to top off the battery after a bulk fill threshold and also levels the individual cell charges. Essentially the charger will deliver say a slightly high constant 13.5 volts regardless of the amps consumed (again by ohm’s law). This is designed to keep filling up the charge kind of like topping off your fuel tank after the bulk fill at full force. You are at a higher pressure (volts) but the volume (amps) will be low. This pushes every last amp back into the battery. After yet another threshold a true maintenance mode (not trickle charge - that was constant amps) is entered that is another constant voltage level a bit lower say 12.5 volts. Again using the fuel tank fill analogy, this is kind of like adding a drop of fuel only when a drop evaporates. This mode can never cook a battery as it is only toping off what the battery naturally loses just sitting there. But wait, there is more… Alas there is one more fancy mode in premium chargers called de-sulphation mode which "shocks" the battery (like you "shock" a chlorine swimming pool) with very high voltages say 15-16 volts for a period of time (sometimes many hours) which loosens the sulphation (the white crunchy growth you hopefully do not see on your plates) and causes it to recombine with the acid. This mode will cause rapid "boiling" and is part of the mix-it-up idea key to de-sulphation.

What’s even better is it all depends on what type of battery you have! Flooded cell (lead acid and most common) deep cycle batteries have different values than flooded cell “cranking” (under your car hood battery), is different than AGM, is different than Gel batteries. But you should only have flooded cell deep cycle or AGM types in your house battery bank. Note flooded cell can also be no or low or regular maintenance varieties and are essentially the same except for usually cap design.

With all that said - the correct “output” be it a certain amperage and/or a certain voltage will depend on the charger manufacturer specs and which mode (if applicable to your charger) the charger is in and what type battery you are charging. Not a simple answer to what in the good old days was a very simple question. Your water usage situation is not all that out of line and just using the house switch trick more frequently might be all you really need to do to extend the fill interval. The automatic thru the caps refilling system is pretty nice but as I recall pricey at some $50 for 6 or so caps. Camping World has them I think. Best advice of all is to keep the water above the plates. Exposing the plates even for a short time will destroy a battery fast.

Happy electrons…

-- Edited by RVDude at 21:14, 2006-09-12

Check what kind of converter do you have?  If you lucked out as we did it will be a progressive dynamics 91xx.  If you have one of these you can get a charge wizard. This is a $25 item that plugs into your coverter and turns your converter into a smart 4 way charger. Go to this website and read about it. It really does work and we rarely have to add water to our batterys.  www.progressivedyn.com. 

 

It's amazing that after almost 8 months, I'm still doing "stupid Newby" things.
The IQ Smart Charger attachment arrived yesterday and I eagerly went to install it. It's a simple plug in to what appears to be a phone jack on the converter. When I looked closely I saw a small label that read Dual Voltage Jack Disabled. Thinking that I maybe had to modify some wiring, I called Iota technical service and they told me that that label means that the Smart Charger option is already internally mounted in original manufacture, so the label is affixed to prevent doing what I was attempting.
Duh!!! I had it already and didn't know it.
So I guess my battery water usage is as good as it's going to get.
Apology to Carriage for thinking that they took the cheap route, and thanks for everybody's help on this.
Fred