One point I failed to mention is that no matter how many cells you use the idea is NOT to let the pack voltage drop below and average "volt per cell" value which many (but not all) believe should be 1.2 volts per cell. This would mean a 4 cell pack should be recharged at 4.8 volts and a 5 cell pack at 6 volts. A freshly charged pack will read higher than these numbers. This is done for the health of the cells in the 6 volt packs.