It can fill 10 pieces of 21700 power Li-ion batteries. But this is plastic shell, there is no battery inside. This product is component without battery core. It is used to repair and assemble batteries pack, only for people who are familiar with battery performance and have practical experience in battery assembly. Suitable for-original (for Devon) 20V Lithium Battery. Functional: High temperature protection for charging and discharging, low temperature charging protection. Overcharge detection protection. Overdischarge detection protection. Three stage overcurrent protection. Short circuit protection function. Notes: After combining the battery pack and this protective board, if there is no voltage output during the initial power on, please activate it with a dedicated charger. Precautions for use and assembly: 1) When welding battery leads/sampling points, be careful not to connect them incorrectly or in reverse. If a wrong connection is found, the circuit board may have been and needs to be retested before it can be used again. 2) During assembly, the BMS should not directly contact the surface of the battery cell to avoid damaging it. The assembly should be firm and reliable. Preparation before assembly: (1). If a core is used, please note: a. 21700 power lithium battery core must be selected b. A group of 5/10 cores must be equipped with resistance and capacitance to make their voltage the same. (2). If the old battery is repaired, please test the voltage at both ends of each cell. If the voltage is different, please charge each cell to the same voltage value. Note: 1. PCB color may be any color according to our stock 2. PCB design may change with the same function and performance guaranteed. Note:Due to different production batches, some accessories have different colors and appearances, and their functions are the same; The color of the protection board is random