> Lithium ion batteries have a much flatter voltage curve - they basically give a stable 1.2V until they run out of juice and then drop rapidly. Did you mean N

> Lithium ion batteries have a much flatter voltage curve - they basically give a stable 1.2V until they run out of juice and then drop rapidly. Did you mean Ni-MH (and possibly Ni-Cd earlier)? Lithium based rechargeables are usually not in AA format and the voltage is closer to 3.6V.