If I am right the stock battery is 600 mah Nicad?
Yes field chargers do charge faster but are not good for the battery.
Nicad batteries will set a memory if not discharged before charging and you will loose capacity.
I recomend a battery conditioner such as a Hobbico Accu-Cycle:
http://www.hobbico.com/cyclers/hcap0260.html
To restore the capacity of your battery.
I replaced my stock battery with a 2100 mah Nimh battery. I only have to charge it about every three or four days and it doesn't have the memory problems of the Nicad batteries.