Molicel P26A 18650 Li-Ion 2600mAh battery.
A very excellent quality, reliable Lithium 18650 battery that gives consistent performance and recommend for box mods, not mechanical.

Key Specifications:

• Format: 18650  
• Capacity: 3700 mAh  
• Chemistry: IMR (Lithium Core Technology)  
• Continuous Discharge Current (CDC): 20 A  
• Pulse / Maximum Discharge Current: 35 A (some listings note ~30 A peak)  
• Nominal Voltage: 3.6 V / 3.7 V  
• Maximum Charge Voltage: 4.2 V  
• Positive Terminal: Flat top  
• Dimensions: Approximately 65 mm length × 18–18.3 mm diameter (minor variations reported across sources)  
  Weight: ≈ 48 g

 Advice:

• Do not heat above 100℃ or 212℉.
• Battery may explode or catch fire if mistreated.
• Do not disassemble or incinerate.
• Do not expose to water or fire.
• Do not short circuit.
• Do not place loose batteries in a pocket, purse, or other receptacle containing metal objects
• Do not over-discharge/overcharge, if allowed to drop past 2.5 volts, chargers will no longer be able to charge these batteries.
• Keep away from children