I am relatively new to ham radio. I am wanting to build a base station
in my bonus room and use some mobile radios up there.

Is it feasible to build my own power supply? I know one radio requires
13.8 volts and a minimum of 12 amps. I would like to use more than one
radio though.

What about buying one of those cheap emergency jump start pwer cells
you can keep in your car. Could I just use one of those and keep it
plugged into the wall charging at all times?

I like the idea of building one but not sure if it would cost more that
way or not. What would I need to build one besides a transformer and
rectifier?