26650 batteries are rechargeable lithium-ion cells. They are also known as also known as 1/3 AAA batteries.
26650 cells can generate high voltages while being safe and energy efficient. This makes them optimal batteries for high-powered LED flashlights, e-cigarettes and radio controlled devices.
You can find rechargeable 26650 batteries by the Chinese company Luangyutl on Amazon.
Battery Junction also has a good selection of rechargeable 26650 batteries.