actual techish question

[glitch@xxxxxxxxx]

I know this is a newbie-ass question, but I have faith that most or all will 
know the answer. I have an at&t craft test set, but no charger. The charging 
is done by plugging a power brick into the unit and leaving it overnight. I 
can buy the charger for $50 online, but I don't have a spare $50 for a 
novelty item like this, so I need to build a charger. That's fine, but 
here's the catch. The battery is 4.8 volts, 500 MAH. I can get a charging 
unit that already does 4.8v but what do I need to use to keep the ampage 
down to 500mah? 
-- 
--dan