Battery protection board is mainly for rechargeable battery (generally refers to lithium battery) to protect the integrated circuit board. The reason why lithium battery (rechargeable type) needs protection is that the material of lithium battery itself determines that it can not be overcharged, over-discharged, over-current, short circuit and ultra-high temperature charge and discharge, so lithium battery will always have a protection plate and a current insurance device. PTC: positive temperature coefficient thermistor; NTC: negative temperature coefficient thermistor, when the ambient temperature rises, its resistance value decreases, the use of electrical equipment or charging equipment can react in time, control the internal interruption and stop the charge and discharge; U1 is the circuit protection chip and U2 is the two reverse MOSFET switches. Under normal conditions, the CO and DO of U1 of the panel output high voltage, both MOSFETs are on, and the battery can be charged and discharged freely.