One way to work around this (and the way cameras do it) might be a power adapter that uses the battery connector. That should even be reasonably DIYable. 3.3V

One way to work around this (and the way cameras do it) might be a power adapter that uses the battery connector. That should even be reasonably DIYable. 3.3V power supplies are readily available, and that voltage matches a (nearly empty) Li-ion battery. Make it beefy enough to handle peak currents at startup, add some minimum circuitry to satisfy the phone's charger and battery protection, and you should be able to run phones and tablets indefinitely. Edit: some reports on stackexchange about people using this setup: https://electronics.stackexchange.com/questions/309886/how-to-power-a-phone-with-no-battery-properly https://electronics.stackexchange.com/questions/309886/how-t...