Twelve Volts, Cheap

When I was working on the Volvo M41 overdrive transmission as documented in the Beck TD blog posts (Parts 51 through 57), I had need of a power supply that supplied a LOT of current - 20 to 25 amps at a nominal 12 volts - to actuate the solenoid that made the overdrive engage. To get there, I just used the battery from the car, which worked great but is an obvious inconvenience to remove and carry over to the workbench. I resolved to find a better solution...