When I need a power supply for something, and chargers are variations on a power supply, I find an old transformer type "wall wart" (voltage adapter as used by phone machines, etc.) and attach an LM-317 variable voltage regulator chip. These can be configured to put out any DC voltage from 1.2 to 32 volts as long as the source voltage is at least 1.2 volts higher than the desired output voltage. There is a formula on the back of the blister pack that you can factor to get the unknown resistor value right, or spend a couple of extra dollars and get a potentiometer so you can dial in the voltage you want by turning the knob. (You will need a voltmeter for this.) The first reference resistor is to be in the 240 - 270 ohm range. Attach a piece of aluminum for a heat sink and you are good for 1.5 amps in output current. For most chargers you will want fewer amps and a current limiting resistor would be in order. Then all you need is a jack for the charger to fit the item you want to charge.
I do not do this with NiMH batteriesbecause they require a "smart charger" that can sample the batteries and prevent overcharging. I also found an LM-317 does not work with the newer switching mode power supplies, only the older transformer power supplies. The switching mode are smaller and lighter. The transformer type are larger and heavy.
LM-317 variable voltage regulators are available at Radio Shack and many other electronics supply houses. If almost none of what I wrote makes any sense to you, you probably do not want to try it. But, there are many electronics tutorial sites on the Internet where utilizing the LM-317 is covered in some detail in order to be helpful to people who want to learn.