Hi,
There are many types of chargers for SLA batts. If it were up to me, I would get an old 3A Lambda comercial built linear power supply, a series isolation diode, so if the power failed, the battery wouldent try to load into the p/s.
I would set it to the 'float' charge voltage the batt OEM recomends, AFTER the diode. Remember diodes exhibit voltage drop. Three amps should be enough so you don't cook it after a discharge cycle.
Use a good DVM.
Current will be limited by the ability of the p/s to deliver. If the draw exceedes the ability to regulate, the p/s will deliver 3 amps (constant current mode)until a voltage threshold is crossed, then it will be in Constant Voltage mode.
If your not using transmitters near by, a Lambda OVP (Over Voltage Protector module) crowbar unit will protect your battery should the p/s short.
Check out Ebay under Lambda, or ham flea markets. You will see a huge amount of used but working units avalable. Also check out the OEM web site. If you ask nicely they will sometimes send you free repair parts.
These are not radio shack or consumer class units.
Most have a feature called 'remote sensing'. This takes some getting used to.
Remote sensing allows the power supply to regulate voltage after the cable losses at the input to the load. I have gotten many bargans on 'dead' supplys, and strapped the S+ to the + and the S- to the - and gotten it working again.
Some are also high precision regulators. .1% or better some times can be had for cheap!
Lambdas are built like tanks. And can be had cheeper than most consumer goods.
I had a 12v 20 amp unit on a ham repeater for many years. I could not kill that thing. We used to 're transmit' the space shuttle audio on it. That thing would be key down for many hours a day, and all it did was get warm. Blowing dust out of the heat sink hardly counts as maintainance.
Enough said.
Keep it warm
Jack Crow in Iraq
