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Most consumer devices that have lithium single-cell batteries have 4 connections. I've noticed the following diverse types of devices, this is true:

  • Samsung smartphone with removable battery
  • GoPro camera
  • Laser barcode scanners
  • Nikon DSLR camera

The 4-connection rule seems to hold even with devices that have multi-cell batteries like cordless drills.

Fundamentally, a battery (or single cell) only needs two connections for the battery positive and negative. But what are the other two connections? Thermistor connections to monitor temperature? Signal wires to an embedded protection circuit? If so, is there any standard or typical protocol? Why always 4 connections?

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Usually two terminals for the power (+ and -).

Then the other two for a temperature sensor / control, often the middle ones.

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  • $\begingroup$ right on Solar Mike $\endgroup$ Dec 24, 2022 at 22:12

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