Measures to solve battery reverse connection.18650 li ion rechargeable battery

　　All battery powered systems have always had this problem: you mistakenly installed the battery, reversed the positive and negative poles, and generated a reverse polarity event. The system is temporarily malfunctioning or permanently damaged.

　　Customized batteries designed to fit the system they are assembled with can help minimize the chances of incorrect insertion and reverse polarity, but proven and reliable ready-made batteries such as AAA, AA, C, and D single cell batteries, as well as CR123, CR2, and button lithium batteries, are also prone to malfunctions.

　　In the past, designers used mechanical structures to avoid electrical contact with battery terminals (if the battery was not inserted correctly). But mechanical solutions are far from perfect. They usually require special processing because spring contacts require well controlled mechanical component tolerances to ensure good contact when correctly inserting the battery, but do not make contact if not inserted correctly. These narrow tolerances can lead to long-term stability issues, as the necessary springs and contacts may bend or malfunction. Even normal use, repeated normal insertion, may lead to contact fatigue and limit reliability over time.

　　However, despite these limitations, mechanical solutions have always existed as they are the only practical solution that designers can use to prevent incorrect battery installation. The electrical solution designed to prevent reverse polarity events caused by inverted batteries has always been controversial.

　　Due to the voltage drop during normal operation, the use of series diodes is usually not chosen. Using a diode grounding setting is not a good idea either, as reverse polarity events can cause dangerous battery discharge to persist for a long time and cause the diode to overheat.

　　Split MOSFETs require complex structures and may not have been optimized or specifically designed to prevent reverse polarity. The key specifications for evaluating performance during reverse polarity events may be lost, and this may force designers to derive estimates from performance characteristics on datasheets and speculate on safe working time periods, which is a concern. Moreover, depending on the application of MOSFETs, they may require a controller or other expensive functions.

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