A dual pack at 2.4v actually needs about ~3.6v (give or take) to charge properly.
Using Alkaline batteries, in a generic pack with no regulation on current is a BAD idea (which is likely why you had bad things happen).
My suggestion is to find an AC Adapter, rated higher than 3.6v (but try not to go too much over) and at 500mA to 800mA. This will give you a nice, SAFE and CONSISTANT charging environment.