Most regular car batteries are good for about four years (especially in
cold weather climates) before they should be replaced with new
batteries,so if the battery in your vehicle is about four years old and
still in good condition and if you live in a cold weather climate,why
not use the old battery for your radio(s) and buy a new battery for your
vehicle? I don't know for sure,but some computer back up battery
units/systems (I use an APC model 1000 computer backup unit for my
computer www.apc.com) just might have a connection on them for 12
volts D.C.current,it's worth cheking out.You could rig a couple of wires
directly (with a proper fuse,of course) to the battery in your battery
computer backup system.I think.
cuhulin