SAMSUNG 3.7V 18650 3500mAh Li-Ion Rechargeable Battery

These high performance 18650 lithium ion 3.7V batteries offer high performance and long life from a compact package. They are 18.6mm in diameter and 65mm long.

Lithium-ion rechargeables offer excellent properties for use in consumer devices, including excellent energy density and low maintenance. Lithium-ion do not suffer from memory effect and possess no regular cycling that batteries often require to extend their service life.

Common applications for 18650 cells include:
Laptop computers
LED flash lights
Electric vehicles
Power tools
Converting AA or AAA powered products over to higher performance (providing voltage  matches).