Hi there SD and welcome!
I'm pretty sure the A23 is just another
manufacturer of the MN21/23 battery.
The different companys name their batteries
slighly different, but they are pretty much
the same for most cases ( maybe not all ).
Anyway, 40mAh isnt all that good, but it
does in fact work. If you have a single
LED flashlight that is drawing 20ma that
battery should last about 2 hours before
dimming out somewhat. Its hard to say
exactly what happens after that because
it depends on the way the LED is driven.
A simple series resistor works very well,
and as the battery voltage dies down, the
LED draws less and less current. Although
this condition means you dont get the bright
light you once had from the new battery, it
does mean that as the battery dies down the
current draw also dies down, so the battery
lasts longer then when the LED is driven
with a constant current circuit. Of course
the light isnt as bright then, but sooner
or later the battery dies down anyway
So you end up making the choice of going
with the larger flashlight that lasts very
long, or the smaller flashlight that cant
last as long, but is more compact.
If you only use it for short periods, like
for a key light, you can still expect it to
last for quite some time because it takes
a while to accumulate 2 hours run time with
a key light.
Here's the thing to do:
Convert the flashlight with the small battery
and use it for whatever purpose for a little
time period, then make another decision:
if the time period for the battery seems
way too short, go to a slightly larger
flashlight that can hold a larger battery.
If that doesnt work out either, go to a
still larger flashlight.
If you intend on running the A23 flashlight
for long periods of time, it may not work out
for you, but you should really try it first.
Good luck with it,
--Al
