Unprotected, flat top (buttons protrude enough for cells to be used in series!)  Sold individually.

This is Efest's "balanced" 26650 option.  It is great for high discharge applications where a bit of extra capacity is wanted.  This battery used to be green, but is now purple.  

Specifications:

• Diameter: 26.4mm
• Length:  66mm
• Nominal Capacity: 4200mAh
• Maximum Discharge:  50A pulsed; 20A continuous.