An 18650 is a lithium ion rechargeable battery. Their proper name is “18650 cell”. The 18650 cell has voltage of 3.7v and has between 1800mAh and 3500mAh (mili-amp-hours).
There are two types; protected and unprotected. We absolutely recommend protected 18650 batteries. The average 18650 battery charge time is about 4 hours. Charge time can vary with amperage and voltage of the charger and the battery type.