Thanks for the input. I'd appreciate any tangible data you have on the subject. As you'll all be aware, claims of performance and safety in the wonderful world of battery marketing are a step up from completely meaningless, though the general online consensus seems to heavily favor LiFe's for safety. For instance, I'd be interested to know anyone's thoughts on: http://electronics.stackexchange.com/questions/172002/lifepo4-vs-lipo
They also are said to have a much longer charge/discharge lifespan, which would be fantastic, obviously. I believe my next step may be to get my hands on a few of these for some destructive testing, including thermal, electrical, and mechanical.
Fortunately for the design, the sturdy casing would do a lot to minimize mechanical trauma, and the current requirements are not high, both charge and discharge should be slow.
The requirement, as it currently stands, is over 3.1 volts, and that it be able to run for one day's use (call it 12-16 hours) on one charge. The microcontroller I am building it around has a sleep function, which consumes somewhere between 10 and 100 microamps. Any moment I use it, however, it will consume much more, for a couple reasons.
I imagine it being used a few times per hour for several seconds each time, and during that time may consume anywhere from half a watt to about 5 watts (150mA to 3A, if you prefer). I believe it could likely be kept under about a quarter watt though, at least when not being charged.
Heh, thanks for that. I admit I hadn't gone that far with that math. Lot of parts coming together at once. Looking around I've found one Lipo which is 30*40*1mm, which is about the perfect size I think, and is 130mah. I think that's about as big as I'd like to go. Shouldn't be too big a problem to keep it down to less than 1A while in use. I can't seem to find LiFe's that are even near that size so far, though :(.
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16 hours @ 0.1 mA = 1.6 mAh for the standby
5second 3A pulse, 5 times per hour = 333 mAh
So you want a 400 mAh lipo.
The 125mA case gives a 17mAh battery.