Nominal voltage is cell voltage. For NiCd, cell voltage is 1.2, thus 12V NiCd
has 10 cells. For alkaline, cell voltage is 1.5, fresh battery is 1.65, dead battery
is 1.2. Thus a fresh 9V battery is at 9.9V while a dead one is at 7.2V. Battery
is dead when at 80% of rated voltage. If take a rechargeable below 80% will damage
cell. Bring your DVM and periodically check your batteries.