Len wrote in message ...
I experience a very short battery-life and I want to know the cause
before I install anything new.

How short?


The fridge / freezer and other consumers constantly draw power
(between 4 and 11 amp)

sounds familiar.....

I have a 3-stage 120 amp charger (bulk at 14,4,absorption at 13,6 and
float at 13,0)

good.

My batteries are 18 months old. 6 x 180 Ah.

I am not familiar with a battery that is 180 amp-hours. What make/model are
these?

Is this six 12 volt batteries all in parallel?
Three sets of two 6 volt batteries?
six individual 2 volt cells?

They were called "Maintenance-free". As I understand now that means you
can't add
destilled water later on, don't see any advantage of that.

Yep. My translation of "Maintenance Free" is "Can't Maintain".

If you keep the charge and discharge rates low then the maintenance free
batteries work. They work just fine in your car. Where they typically
don't work is in a deep cycle application where the charge rates can be very
high.

On many of the maintenance free batteries you can gain access to the cells
but you have to work at it a little harder. They have a battery cap, it is
just a little harder to get off. Other batteries the caps were put on in
such a way that you will not be able to get them off without really messing
it up.


Anyone familiar with such problems that (maybe) arise from using the
charger as a power supply during float-charging?

The type of charger you have is about the best you can get.

I suspect that you are in a different country than I am (I am in the USA) so
your choice of batteries might be a bit different. Here in the USA, the
most common use for deep cycle batteries are in Golf Carts. The standard
golf cart battery is easy to come by and fairly cheap, in fact they are
commonly found for less than an equivilant automotive battery. And they are
rugged: if you keep water in them they will last 5 years or more.

My advice is to dump the "maintenance free" batteries and go with the good
old "golf cart" batteries. In the USA, these are 6 volt batteries that are
in a case style that is referred to as T-105 or 2200. They are 10-3/8" long
by 7-1/8" wide by 10-7/8" tall, compared to the 27 series which is 12-3/4"
long by 6-3/4" wide by 9-3/4" tall. Connect two of these in series to get
12 volts. Connect as many of these sets in parallel as you need to get the
desired amp-hour capacity. One set of these batteries will provide you with
about 225 amp-hours each.

Good luck
Rod McInnis