ORIGINAL: DMcQuinn
I would encourage you to go ahead with the 5-cell pack. 99% of all servos made will work OK with 5-cells. And your standard charger will also work OK - it will just take longer to charge than if you used a 4-cell pack.
I am sorry but you are wrong. A wallwart charger designed to charge a 4.8 volt battery can not be used to charge a 6 volt battery. The charging voltage has to match the battery being charged.