How to know if your wall charger will work with your new set of batteries?
Follow this rule:

Your battery is 4.8 Volts
Capacity is 750 mA

1.- Option “A”; Your wall charger has an output (receiver) 5.8 V ~50 mA (old wall chargers)

2.- Option “B”; Your wall charger has an output (receiver) 5.8 V ~150 mA (new wall
chargers)


Think that your battery will be fully charged when it reaches the capacity of 750 mA and also think that at any charge there will be a loose of about 15% of the capacity of the battery, then at the end you have to calculate the capacity of your battery as a 750 + 112.5= 862.5 mA

If you use the option “A”
The equation is: 862.5/50=hours of charge
Then the result is 17.25 charging hours.

If you use the option “B”
The equation is: 862.5/150=hours of charge
Then the result is 5.75 charging hours.