Do the math.

A wall wart charger output with (say.. for example) 50 ma output, and a 1000 mah battery.. divide the 50 into the 1000 and you will get.. 20 hours. Add 20% overhead (heat and other overhead) and that is the amount of time to fully charge the battery from completely drained.

The wall wart battery charger is also a trickle charger and will top off the battery in a few hours (as said above by several others). If you have any doubt or questions, put it on the charger, overnight if necessary. You won't hurt it.

CGr.