Can the particle electron be powered with an 18650 battery? Or does it have to be a lipo?
Same chemistry, just different construction.
Some cylindrical cells don’t have protection circuits built into them (some do).
So yes? Ok thanks!
Yes, I’d suggest use a quality Protected 18650 cell.
Would i be able to use a lipo AND an 18650 to power the particle electron? to extend battery life?
Try just use a higher capacity single cell battery with a protection pcb attached to keep things simple and to prevent cell miss match issues.
You can power it with any battery you wish. However, if you are simply plugging into the battery port with another battery then make sure it is a 3.7v. I have had great success using this: https://www.adafruit.com/product/353 which +/- connector matches with the electrons. And the pmic seems fairly accurate still.
You can also power the electron with a 12v battery by using the VIN pin, however, you will need another way to guess battery health.