If you want to go that route, I can talk you through it. You will need 2 female banana plugs (radio shack is a good place to get them)

You will also need to be ok with soldering and taking apart the PS.

What types of batteries will you be charging? Voltage and mah. Also what charger. That all makes a difference to how powerful of a PSU you need.

This would be a good starting point. I have one of this brand, but lower wattage.

You want a single rail PSU. the multi rail ones wont work that well.