8.4V's woohoo we have an answer! It's a 7 cell pack =) I'm not sure why you're using such a battery pack, lithium batteries are better in every respect of operations for small packs like that. Seeing a battery voltage over 8.4 volts on a freshly charged NiMh pack is perfectly normal, that 'surface charge' quickly goes away when the battery is actually loaded. Use google to search the net or the forums here, there are MANY threads for charging battery packs that include charger schematics.