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Is it possible to charge the embedded battery in DJI Tello while the drone is powered on, in any state? Eg restart, emergency, landed

For example, when I want to keep taking photos (without flying), but to keep the battery full without replacing it or to stop filming

Every approach is accepted - app, network protocol, break the device.

In the original User Manual it says

It cannot be charged when it is powered on

However, I really want to be sure I’ve checked all the options

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Charge controller solution

Many (cheap) charge controllers have difficulty both charging and providing power at the same time. Look into how solar/off-grid guys do lithium charging (you need a specific type of charger). You'll have to hack the backside of the BMC on the battery so that it doesn't lose its mind from unexpected flow. The BMC might also not allow this at all due to the fact that you're pumping out more capacity than the battery ever had.

PSU take-over solution

Build a power supply that starts disconnected, and uses some sort of detect-and-latch to detect the exact voltage on the power bus, latch onto it, and then provide that voltage (-0.01V so as to sink instead of source, for the time being). Once your PSU has latched and matched (nice catch phrase), you can safely remove the battery. The ADCs on board won't care (or even notice) for millivolt-level fluctuations.

Some care will have to be taken here as once you then plug in a fresh battery, there will be a significant voltage differential, and the power supply will have to be built such that it doesn't accidentally sink all of that current and kill itself.

Caveats

  • Cleanflight/the original multiwii relied on internal counters to do timing. As such they would time-out relatively quickly (36 hours I think?). Hopefully anything DJI makes is 32 bits so even in milliseconds, you're covered to sustain for a few days.
  • The internal flight controller might also track mAh consumption. Once this exceeds how much the battery originally told the flight controller it can put out (I wouldn't put it past DJI to make smart BMCs), you might end up in a limp-home mode that only a full reset can escape.
  • I have no knowledge of this specific hardware, this is all based on general design assumptions given knowledge learned in the field.
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