I suggest getting a gell cell to avoid battery acid spills or fumes. I
only use mine when in the field, so I don't have a set up as you
suggest. I charge my battery from a bench supply using 13.8v as a
float voltage.

Depending where you live, you may find used gell cells that are part of
a data center backup system. These batteries live indoors and spend
most of their life on float (OK for SLA batteries) and maybe once in a
while provide backup. Alarms use similar style battiers, but not very
high capacity. The Yuasa NP7-12 is a real common back-up battery. It is
only 7 amp hours, but what you might do is get two of them, keeping one
on the charger while you use the other. Typically in alarms or data
backup, the batteries are replaced on a schedule rather than waiting
for a failure, so there are plenty of free or low cost batteries
available.

If you don't want to use a bench supply, West Marine sells all sorts of
chargers, though a bit pricey.

bpnjensen wrote:
Hi, folks - I would like to try running my Icom R-75 at home from a 12
- 13.8 volt cell or battery. The requirements would be that the cell
would be able to recharge from 115v AC during the radio's off time, and
that while the radio is turned on, the battery would be electrically
disconnected from the wall AC. It does not matter to me whether this
connect / disconnect is manual or automatic.

This device might also run an MFJ Noise Canceller unit, which uses
lower voltage (I would need to provide a step-down for this device, or
a separate battery).

I would like the battery to be nice and big, something that would
provide an easy constant 36 watts (12v at about 3 amp max) for several
hours straight without strain. It would be nice if this device did not
develop a memory (no NiCads, please). It would be nice if it were not
an ugly thang with potential leaky chemicals like a car battery.

Can anyone recommend such a set-up, and/or some specific manufacturers
and model nos. that might fill the bill?

Thanks so much ~
Bruce Jensen