Maybe? Could use a power source like a computer that converts 110 to 12v... I`ll google it more

In order to maintain a seldom used battery in good condition, there are two options.

The first one is to install a PV module and charge controller, a relativly small module will suffice since the intention is not to recharge a flat battery, but merely to counteract self discharge.

The second choice is to purchase a line powered battery charger that is fully regulated and suitable for continous operation.
A constant voltage float charger is preferable to a three stage unit for this purpose.
The drawback of a line powered charger is the continuall small power useage which will increase your electricity bill.

Whichever option is chosen, you will also need a high capacity line powered charger to fully recharge the battery after a grid failure.

Traditional flooded lead acid batteries produce hydrogen when on charge, and therefore some experts state that they should never be used in living accomadation.
The amount of hydrogen produced is very small, provided the batteries are not overcharged, and IMHO one or two small batteries can be used indoors, provided that smoking, sparks and flames are kept away from the immediate area.
Remember that until very recently, disabled people used electric wheelchairs with flooded lead acid batteries. These were normally charged and used indoors without accident.
Also many domestic garages are used as workshops, without the vehicle battery being considered a risk.

Sealed batteries dont produce hydrogen in normal use, but may do so in case of failure or misuse.

I'm looking at this myself. I want to use a solar charge controller, it takes 12-15v in and regulates it and mnitors the battery charge. Gte one with a low voltage disocnnect output. Normally this is used to open a relay to disconnect the batteries from the load, but instead of that use it to switch the input from solar to line power. So if the solar or whatever can't keep up with the batteries the lvd output turns on the line supply.

Right...

Part of our mission at Hanford included building a portable trunked repeater system for use in case the main and secondary site went down, or if we needed extended coverage and/or mutual aid support. We built the system on a flatbed trailer with all the goodies housed in a big poly coated steel box. We had a battery bank capable of keeping the whole system up and running for 72 hours, with a nominal power consumption 350 watts. We used deep cycle batteries as opposed to automotive type because we did not plan on running the system in a constant charge mode. We used a Marine Charger/maintainer to keep the batteries at full optimization while on standby, which was most of the time. The unit cost about $500 and was pretty smart about how to keep those batteries in prime condition. I believe Xantrex makes some of the best charger/maintainers on the market these days. Deep cycles are great for when you need to run on batteries for a long period between charges. Automotive batteries work better when you running in a constant charge mode (as with wind and solar generators, or floating the batteries on a live circuit). Deep cycles like to be fully discharged every so often, and the system we used took care of all that to keep the batteries in perfect condition.

I have seen a recommendation of golf cart batteries. I am told that they are deeper cycling than other batteries. The draw back is they are 6 volt so you have to use them in pairs with each pair wired in series and then parlled to addtional pairs.

Oh, there are hundreds of different battery configurations one could try. Ultimately it pays to do some research, determine what you need, and shop around a little. Golf cart batteries, like most others, are built for a purpose, and may not lend themselves so well to others as much as ones who were designed for an intended purpose. Yes, they will work, and maybe work quite well, but it is easy enough to find the battery that suits your needs in particular.

I have been working with a system of 3KW xantrex inverter/chargers coupled with 4 12v deep cycle batteries to power pet grooming vans. batteries are charged at night by being plugged into the grid, and by day through a big inverter on the van. They have worked all day every day for 2-3 years with no major prob;ems.

Bingo!