i've used open frame regulated power supplies to charge car batteries. first of all, they're cheap (usualy about $10.00 if you actually have to buy one). they usually have very stable foldback current limiting, and usually have a voltage adjustment as well as a current limit adjustment. if the voltage adjustment doesn't have enough range, you can fool the power supply into giving you enough voltage by putting a couple of forward biased diodes between the output terminal and the sense terminal. i have one that's rated at 12V@10A. i have two diodes between the +out and +sense terminal, which boosts the nominal voltage up to 13.5, and the voltage adjustment will now max out at 14.5, so 13.8 is within the adjustment range. the current limit is set at 6A, and will give a rock solid 6A even into a short without any ill effects to the power supply. if you know somebody that does industrial equipment repair, they probably have a few of these laying around, usually with a shorted overvoltage protect circuit. the protection circuit is usually a crowbar circuit (an SCR triggered by a zener). usually just removing the SCR from the circuit restores normal operation of the power supply. in many cases the crowbar circuit is a little add-on board anyway, and can be removed. the crowbar is there to protect the end user's equipment from power surges, and since the application doesn't require such protection, the crowbar is unneccesary.