Lead acid and NiMH require different charging regimes. Lead acid needs a slow trickle charge while NiMH needs monitoring of the temperature of the cell and the change in voltage to keep from harming the battery. Batteryspace has some inexpensive smart chargers that will save you money in the long run and charge faster.
I'd also suggest you look at this battery. Same capacity but cheaper. You can get the proper leads to retro fit your lights to the battery at any hobby shop that carries RC cars or on-line. Pretty simple wiring really.