Also bear in mind that "6 volts" is not the same to everyone!
6 volts is actually 6 volts, but some people (a lot, actually) erroneously refers to a 5-cell NiCd or NiMH pack as a "6 volt pack".
However, fully charged, these packs are more than 7 volts. (Probably around 7.25 volts.)

Magne