About the K1 charger:
The Keeppower K1 Battery Charger is a versatile charger that can be used to charge a wide range of Li-ion and Ni-MH rechargeable batteries. It features a Type-C input port and an LED indicator to show the charging status. The charger has a current switch that allows you to select the charging current for different battery types. It is compatible with Li-ion batteries such as 26700, 26650, 26500, 21700, 18650, 18500, 18350, 17650, 17500, 16650, 16340, 14650, 14500, 14430 and Ni-MH batteries such as AA, AAA, A, SC, C, and F6. The charger has an input voltage of 5.0V and a current of 2.0A. The output voltage is 4.20V for Li-ion batteries and 1.48V for Ni-MH batteries. The output current can be adjusted to 0.5A, 1A, or 2A for Li-ion batteries and 0.5A for Ni-MH batteries. Built-in high-precision MCU and real-time temperature control protection system, with over-current protection, over-charge, over-voltage, and short-circuit protection. The charger will automatically stop charging after fully charged batteries.
About the 18650 battery P1840C:
MODEL: P1840C
BATTERY CAPACITY: Nom. 4000mAh discharge at 0.2C; Min. 3900mAh discharge at 0.2C
NOMINAL VOLTAGE: 3.6V
OVER CHARGE PROTECTION VOLTAGE: 4.2V
OVER DISCHARGE PROTECTION VOLTAGE: 2.5V
OVER CURRENT PROTECTION CURRENT: Above 15A-25A
SHORT CIRCUIT PROTECTION DELAY TIME: 280±84us
STANDARD CHARGE CURRENT: 2000mA
MAXIMUM CONTINUOUS CHARGE CURRENT: 4A
STANDARD DISCHARGE CURRENT: 2000mA
MAXIMUM CONTINUOUS DISCHARGE CURRENT: 8A
MAXIMUM SIZE: 18.8(D)X69.2(H)mm
NTERNAL RESISTANCE: ≤ 50mΩ
MAXIMUM WEIGHT: 49g
OPERATION TEMPERATURE: 0℃~+45℃ CHARGE; -20℃~+60℃ DISCHARGE
STORAGE TEMPERATURE: -20℃~+60℃ Less than 1 month; -20℃~+45℃ Less than 3 month