These are Maxday 18650 Li-ion rechargeable batteries.
Type: Li-ion 18650
Voltage: 3.7 V
Capacity: 4000 mAh
Material: Lithium Ion
Cycle Life: Up to 1000 charge/discharge cycles
Disclaimer: Be sure to use the correct charger designed for these specific types of batteries and follow all safety guidelines for charging and handling lithium-ion cells to prevent fire or injury.