"CMF" writes:
Quit interesting that you said that. Based on some of these posts, I am
going to check the next set of alkalines out of my HP 215. If it has the
same problem, then I bet the NiMH's won't be any better. God I hope not, I
sure would like a rechargeable solution.

You need to measure the voltage under load. That's particularly
important with high-current devices like a digital camera, or a 5 W
radio transmitter. There are some devices where the internal resistance
of the alkalines is the problem, not the design of the device.

For example, suppose you have a digicam that uses 2 AA cells, and it's
been properly designed to operate down to a voltage of 2 V. A pair of
alkalines start out a 3 V, but the camera sometimes draws enough current
(particularly with the LCD backlight on, and when recharging the flash)
that the voltage *under load* drops to 1.3 V. So far so good.

Now, after you've taken a few photos, the alkalines have dropped to a
no-load voltage of 1.3 V - meaning they still have most of their
capacity remaining. But the internal resistance increases as you
discharge the cells. Now, when you take a picture, the high current
momentarily causes the battery voltage to drop from 1.3 V to below 1 V,
and the camera shuts down.

NiCd and NiMH cells have *much* lower internal resistance than alkaline
cells, and it stays much lower throughout the discharge life of the
cells. These cells can deliver several amps of current with very little
voltage drop. So, although a pair of cells produce only 2.4 V, you
still get something like 2.3 V or 2.2 V under heavy load until the
battery is almost completely dead - and the camera continues working.

Basically, if alkaline cells power a device for a longer time than
current NiMH cells, then either the device has very low current drain
(where alkaline still does have more capacity), or the device hasn't
been designed to operate all the way down to 1 V per cell (bad design).
While if NiMH cells operate the device longer than alkaline cells, it's
probably because the device draws lots of current and the alkaline cells
have too much internal resistance.

Dave