I'm trying to finish a very compact project, but I need a battery-powered 5V source and it has proven tricky. I'd like to get 500mA or more, for some IR LEDs (and the controlling Arduino Mini).
I have a Bodhilabs Vpack, which steps up to 5V, but it won't work with a 3V CR2032 or a pair of 1.5V button cells, only AAAs or AAs...
Is there a way to get 5V from button cells from this board? Or, are there small alkaline cells that might work instead of AAAs or AAs?
Thanks in advance for any clues!
Cell phone batteries are small and can produce the current your looking for.
Coin and button batteries are designed for quite small current draw.
We know you need 5 volts at 500 mA. There are (at least) two important figures left out.
How long must it run on battery power, and just how small is the allowable space?
Is weight a factor? How about safety?
The Energizer CR2032 spec lists a couple of operating points -- Continuous operation at 190uA and pulse operation at 7mA. Your operating point greatly exceeds both operating points which is why the Vpack won't work.
Your current requirement is 100 times greater than the CR2032.
(* jcl *)
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Wow, didn't realize how low the cr2032 current is!
The high power requirement is just for short flickers of the IR LEDs, so most of the time I'd just need power for the Mini.
For space, about 2x3x3 cm is all I have to work with. As for safety, uh... I'll be fine?! 
Look into Lithium Polymer batteries or battery packs, but beware because improper charging can lead to mild explosions, fires, and release of toxic gasses. People have burnt down their garages... (improper discharging will quickly leave you with a dead and no-longer chargeable battery that you paid rechargeable battery prices for, as well.)
An arduino-like circuit with some flickering IR LEDs should run OK off of 3 series connected 1.5V button cells (4.5V nominal) without any need to boost to exactly 5V. For example, see the TV-B-Gone circuit from Adafruit.
You can get some lipo batteries that are tiny, but they don't pack allot of capacity, so your run time of your project is going to be really short.
It'd be really helpful to know how often your project fires the IR LED, how much current it uses when the LED is off, and how long you expect it to run on batteries, it's quite hard to recommend a battery without that sort of info, all you've said is how much current it draws when the IR LED is emitting.
You also have to take into account the max discharge that will be expected of a battery, for instance the lipo battery I linked is 150mAh, its "C" rating is 12, you multiply the capacity by the C rating, 150 x 12 = 1800, which means that battery can supply a constant 1.8A, how ever as it's only 150mAh it could only do that for about 5 mins before it dumps (Lipos don't go flat as such, they dump, once it's dumped you should stop using it and charge it)... as a guide, if you want a 150mAh lipo to last for 60 minutes you should be pulling less than 150mA from it.
Another point not mentioned is lipos don't like being "drained" a lipo cell should not be discharged below 2.5v (at very worst case), to be safe they shouldn't be discharged to below 2.8-3.2v, or the cell could be permanently damaged and could potentially catch fire as westfw pointed out.
If you don't mind me asking what does the project do?
Switching back to primary (non-rechargeable) batteries, there are lithium batteries frequently used in cameras. The CR123A is a bit larger in diameter then a AA and a bit shorter, and a single cell is 3V. Delivering current isn't a problem, either. There are other cells even smaller than the 123 (roughly same diameter but shorter), like the CR2(?). There's also a 3.6V lithium AA cell.
All these can be a bit pricey, as compared to alkalines (although they're cheap compared to LiPos and their chargers).
-j
bircoe, the project is very similar to a TV-B-Gone-- waits for a button press, emits some flashes. I use a pnp resistor to trip four npn resistors, just like the latest Adafruit TV-B-Gone version.
Using three button cells to get to ~4.5V might be the easiest route to completion-- enough for a laser pointer should be plenty for my needs. A smaller lithium like a cr123a sounds good too if I the button cells can't swing it.
Thanks for all the information, folks!
