The voltage may not be on there. For lipos a nominal voltage of 3.7 per cell is used , and that will correspond with an empty pack. 4.2 volts per cell is for a full pack. Depending upon how hard the current draw is the operating voltage may be anywhere between 3 and 4 volts per cell. Usually it works out to divide the number of nimh cells by 3 to get the lipo equivellant.

4S column should be 14.8 volts
5S column should be 18.5 volts

You may even want to go with 6S for higher voltage.