If you are looking for an external 18650 battery for their vape device (SMOK RPM 160, Geekvape Aegis Boost Plus, SMOK RPM 2, VOOPOO Drag X) than MXJO is a reputable brand at a competitive price. 

The specifications for this battery:

Size: 18650

Style: flat top

Nominal Capacity: 3500mAh

Discharge Current: 10A maximum continuous, rated 20A

Nominal Voltage: 3.7v

Maximum Voltage: 4.2v

Approximate Dimensions: 18.22mm x 64.89mm

Approximate Weight: 44.8g