The Anatomy of a Protected LiIon Battery

A protected battery will (hopefully) include the following protections: PTC, protect against over temperature and indirectly over current and will automatic reset. CID or pressure valve, will disable the cell permanently if the pressure is to high in the cell (Can be due to over charge). PCB will protect against over discharge, over charge and over current, depending on design the PCB will reset automatic or when placed in a charger. Unprotected batteries are missing the PCB protection, but usual has the PTC and CID. The PCB protection is highly recommended for some LiIon batteries (LiCoO2). Here I am going to show how this PCB is fitted into a LiIon battery. Measuring on the protection circuits I found: AW: Current consumption: 4.5 uA, i.e. it will discharge a 2000mAh battery in 50 years Overdischarge will disconnect at 2.5 volt, but will only reconnect if the battery goes above 3 volt. Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger. Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 25mV The other big circuit: Current consumption: 4.2 uA Overdischarge will disconnect at 2.5 volt, but will not reconnect again except with external voltage (i.e. a charger). Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger. Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 30mV The small circuit: Current consumption: 3.9 uA Overdischarge will disconnect at 2.5 volt, but will not reconnect again except with external voltage (i.e. a charger). Overcharge will disconnect at 4.26 volt and will reconnect when battery is removed from charger. Voltage drop in circuit at 1 amp and 2.9 volt battery voltage: 60mV The above measurements are only valid for the circuits I have measured on, but gives an indication about what to expect from LiIon protection circuits.