Coin cell CR2032
These really DO NOT like current spikes. So a lot of buffer capacitance will be needed to buffer the LED current spike. Data from Energizer:
- 235mAh downto 2V, rated for 190µA load
- Lithium / Manganese Dioxide (Li/MnO 2 )
Battery life calculations show that the project could run about 1 year when ON-current is 5mA and OFF-current is limited to 1µA.
3V CR123A Lithium cells
store up to 1700mAh. These will last a lot longer.
If a rechargeable solution is desired, then the 3.7V/120mAh LIR2450 can be used. This cell tolerates current spikes much better.