I have used many different battery chargers in my lifetime. The ONE that I own now is an ac/dc lipo charger designed for the radio control hobby industry. It will literally charge almost any battery that you own (haven't found a way to charge my 512vdc flashpack battery yet). The only other thing that you would need is a 4c cell holder. Just attach the alligator clips to the + and - sides, set the charger to the required type, voltage, and charge/discharge rate, then sit back and wait. Most batteries charge within 10 - 15 minutes.
On a side note. The minelab is a perfect candidate for a lipo battery pack. Each lipo cell is 3.7v so a 3s pack is 11.1v. Someone could easily build a voltage reducing circuit and use a rather large capacity lipo in the space of 4 c cells. Just a thought.
Trevor