AW LiFePO4 3.2V 500mAh rechargeable battery.  You can use 2 of these batteries in the P18 for 6V vaping.  LiFePO4 batteries use a safer chemistry and do not require protection.

The AW brand is considered by many to be the longest lasting, best quality batteries available!

LiFePO4 Specifications :

• Nominal Voltage : 3.2V
• Capacity : 500mAH
• Lowest Discharge Voltage : 2.0V
• Standard Charge : CC 250mA CV 3.6V
  
• Cycle Life : > 500 cycles
• Weight : 16.5g