tsunamy_boy:
humm then i already have similar to that =)
I would go with a charger that doesn't need changes
You are free to add a tiny board that adds a DIP switch that patches in different resistors.
You are free to add an digitally controlled potentiometer that switches the resistors under keypad/LCD control.
You are free to plug all that into an Arduino with a library of battery specs, that you pick the battery and it knows how to set the digital pot.
Orrrrr you can go buy a charger that already has those features in it. Well, not the library of specific batteries, but you tell it the mA and it does the rest.
Arduino is all about the 'exercise for the student.' If you want to be the student and design/build it, then do it. If you just want the device to use it, then it's already available.