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As the title says, what does the 'C' marking mean? I first figured it may be the terminal that outputs temperature data but I'm not sure. I wanted to build a custom solar charger for this battery and I was hoping to know if this terminal is important in any way.

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NP-FZ100 is the battery supplied with Sony α9, α7R III, α7 III, a9 II, a7RIV, a7S III, a7C cameras.

The terminal marked 'C' is for serial communication to display the remaining charge of the battery on the camera's LCD screen.

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  • \$\begingroup\$ Thanks. Yep its for my A9. However, if I do not need to display the remaining charge, I could just not use the C terminal right? \$\endgroup\$ May 30, 2022 at 6:18
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    \$\begingroup\$ @electrophile yes, it is probably save as long as you make sure your charger does not damage the battery (not drain it, not overcharge it, not charge it with too much current). \$\endgroup\$
    – kruemi
    May 30, 2022 at 6:27
  • \$\begingroup\$ Should the 'C' terminal not make proper contact, an error message would be displayed instead of remaining charge. \$\endgroup\$
    – vu2nan
    May 30, 2022 at 6:27
  • \$\begingroup\$ @vu2nan, I don't need the remaining charge to be displayed on the charger anywhere. My solar charger is likely to be based on TI's BQ24650 which would anyway monitor charge levels. \$\endgroup\$ May 30, 2022 at 6:30
  • \$\begingroup\$ During charging, using the matching Sony charger, the state-of-charge and battery temperature may be communicated to the charger. With only the +ve and -ve terminals connected to another charger, there would be no means to monitor even the battery temperature at the very least. \$\endgroup\$
    – vu2nan
    May 30, 2022 at 7:35
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That's the Sony A7 etc. battery. There is circuitry including a microcontroller inside the battery package. The C likely stands for "communication". Communication is digital. Maybe someone has reverse-engineered it and published the results- as far as I know it's proprietary to Sony.

Sony calls their battery communication system InfoLITHIUM.

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  • \$\begingroup\$ Thanks, this is not a reverse engineering but more like a teardown and some attempts to see how it works. Since the battery is not just the battery but already has some charging circuitry built into it, would simply connecting the + and - leads to my solar charger work? \$\endgroup\$ May 30, 2022 at 6:25
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    \$\begingroup\$ I don't know that it has "charging circuitry" built in. 7.2V appears to be two cells in series. Maybe you could look at what is inside the Sony chargers. \$\endgroup\$ May 30, 2022 at 6:58

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