18650 Cells

https://www.google.com/search?q=18650+cells&client=ubuntu&hs=KUs&source=univ&tbm=shop&tbo=u&sa=X&ved=0ahUKEwj8xPLHwdLfAhULtIMKHTQ3ADUQsxgIKw&biw=1438&bih=738

Specs

• Note actual spec from a buyer on Amazon - [1]

Reviews

• https://thegunzone.com/best-18650-batteries/
• https://www.18650batterystore.com/Best-18650-Battery-Guide-s/142.htm

Management

• Multiple thousands of cycles are possible when charged to 80% and drained to 30%. - [2]

Cost

• From <$1 to $7 each - so choose wisely -
• Cheapest - [3]
• Best - Samsung 30Q - 3000 mAh - $3 in bulk - [4]

• These appear to be on spec at 3000 mAh - [5].
• Cycle life and specs - [6] - 250 cycles to 70% of rated
• 1000 cycles at 6A discharge rate bottoming at about 60% capacity for 2000 cycles? - [7]. So these last pretty long.