There are 2 versions of the 123. Versions with firmware 1.xx have NiCd Batteries. Versions with 2.xx firmware have NiMH batteries. The chargers are the same for both, but be aware if you have to replace battery.
Ron is right about the center negative, watch out almost all bricks are center pos. If you buy an aftermarket charger, make sure it is electrically isolated from the mains (usually indicated by a 2 pin mains plug instead of 3). Otherwise you cannot make floating measurements with it plugged in.
The 2 channels on the 123 are NOT isolated from each other, they share a common ground. Keep that in mind when measuring signals with different grounds.