Rechargeable Battery for PowerFLARM Flex

18650 Battery, Rechargeable, Li-ion, Panasonic NCR18650GA, Protected, Button Top, 3.6V, 3450mAh, Max Continuous Current: up to 10 A (6 A typical PCB-governed),

Length: 69.5 mm, Diameter: 18.5 mm, Weight: 49.4 g

Recommended for the PowerFLARM Flex.  Powers the PowerFLARM Flex for 10+ hours

You can find less expensive 18650 batteries online, but I prefer the quality of the Panasonic brand.  Another reason that I prefer this particular battery is that it is "protected", meaning that it has a protection circuit built-in. Making it more safe than "unprotected" versions.