I suggest you get rid of a deep cycle battery for the starting battery. Use
a regular starting battery, such as is available at any automotive supply
store. They are cheap and are designed for delivering a lot of current for a
short period of time in a starting application.
The combiner, if wired correctly, should be only charging the banks when the
alternator is delivering power. Shore power and the battery charger should
not be a part of the combiner path. They should be two separate, not
simultaneous, charging circuits.
Ensure only the engine is connected to the start battery. There should be no
additional loads on the start battery requiring it to be charged frequently.
Suggest you put a heavy duty ON/OFF switch in the path between the shore
power charger and the start battery. Turn ON only when you feel the starter
battery needs a charge.

Doug K7ABX

"Don WA5NGP" wrote in message
om...
I would be a bit suspicious of the quality of the starting battery.
My experience has been that when batteries get on their last legs (and
need to be changed anyway) that they seem to boil away the water a
lot. It seems that no matter how you stay on top of keeping it filled
it seems to boil away. I suspect that it may be due to sulfation
buildup that creates something like an internal short, heat, and loss
of water.

Good luck
Don

"Marc" wrote in message
...
I suspect something is wrong, but need confirmation. I have three
deep cycle wet group 24's as the house bank and 1 deep cycle wet
group 24 as the starting bank. A 150 amp combiner is installed
between the banks and both banks are connected to individual legs of a
xantrex 20 amp charger.

The boat sits in a slip with shore power connected, charger on, and a
reefer running 24/7 off the house bank.

I am losing electrolyte faster in the starting bank than the house
bank.

Question : Since I have a combiner, should the charger be hooked up
to both banks? Could this be causing the electrolyte loss?