RE: wall wart charger
Wall wart chargers generally have a large voltage range. One that says "9V 100 mA" can be used to charge 9V batteries. But if the same charger is used to charge 4.8 volt battery, it may charge at 150 mA. Basically the design is a current limited design. If you use the same charger to charge 12 V battery, it may only charge at 50 mA.