I'm building a project which needs to fit in a wallet. I have an Arduino Micro hooked up to a nRF8001. I attempted three button cells wired in series, which provided a solid 7.5 volts, but only 20mA.
A 9V battery successfully powers it, but that's too big to fit in a wallet. I was considering using an A27 battery, but even that's thicker than I would like.
Is there any battery I can use that's a reasonable thickness, and won't explode on me? Thanks!...
I think you should use a 3.7v mini battery that are around 200-300mAh capacity. These batteries are variable on online stores and are very thin. Now as you require 5v there are mini DC-DC boost converters available what you can use with them.
You can use rechargeable Ni-Cd batteries of 3 AAA size cells with wired connection.There are also small 4V rechargeable lead-acid batteries,which are mostly used in led torch.
Either of these two are pretty good depending on how long you want it to live and how much current your device draws:
https://www.sparkfun.com/products/731
https://www.sparkfun.com/products/10718
You can still probably power the micro from these even though they're 3.7v. When charged they'll be closer to 4.2v and it will still probably run down to 3.5v anyway.
Or you could just put two in series to increase the voltage
I run my projects directly from a 3v CR2032 lithium cell. Bypassing any voltage regulator. You could use something like a I'd get a 3.3v arduino, something like a Arduino Pro Mini. (You can also use your micro, but you'd have to "underclock" them, as the ATMega32u4 isn't necessarily capable of running 16Mhz at 3V.)
By bypassing the voltage regulator, you don't get any of the losses.
