Please? Your post on other types was great.
QED is correct. I misspoke. 1.4v is the ‘float voltage’ on NiCads (which is the voltage when resting in a good charger) The open cell voltage is roughly 1.25v
Different devices, even of the same general type, are affected differently by lower voltages. Many devices are more sensitive to available current at a given voltage, than they are to the voltage itself. Your usage can be a factor too. For example, going back a few years some portable tape player motors drew far more current for the motors than others, or had less efficient electronics, so players with the same current draw rating might react differently if most of the current went to the motor vs. the circuitry. Similarly, a portable CD player might react differently with different headphones or speakers and/or crank it up vs listening at a low volume. Some devices draw more current when they start up (e.g. bringing a CD up to speed vs. maintaining speed) so they may not start up, even if there’s significant ‘run time’ left in the battery
Energy capacity is rated in Amp-Hours. Technically, it should be Watt-hours (e.g. the kiloWatt-hours you pay for on your electric bill or how long a battery can sustain a given power load), but since Watts = Volts * Amps, and the voltage of a given chemistry is pretty constant across manufacturers, Amp-Hours or milliAmp-Hours work fine. The figures are just for comparison, anyway. Your mileage will vary with things like current drain and start-up currents.
The newest NiMH batteries can have up to 10 times the capacity of most NiCads, and versions with few hundred more milliAmp-Hours seem to come out every few months. Don’t stock up much beyond you present needs; next year’s models will be better.
On the other hand, NiCads may be smarter for infrequent use. They self-discharge more slowly. A NiMH can lose 2-3% of it charge every day it’s stored, and needs recharging every month even in storage, but I’ve had NiCads that were usable after 6 months. A partly drained 700 mAH NiCad is more useful than a dead 7000mAH NiMH. (also, letting NiMH cells sit around dead isn’t good for them)
Whatever your choice, pay attention to the mAH ratings. Don’t buy batteries if the capacity isn’t clearly marked! I’ve seen 700 mAH D-cells next to 7000 mAH D-cells (and it wasn’t a typo) Avoid cheap chargers: they can wreck your batteries, and the inconvenience of missing features alone can make them a bad deal.
Here’s a Round-up of a whole lot of AA NiMH batteries. In short: Maha Powerex batteries are the best, with the Powerex 2200mAh scoring the highest of all. While designed to study performance in digital cameras, I’m thinking that the results will also be generally applicable.