Reply:
Hmmmm. Don't know where you got your information (about a low-battery, or need to charge indication), but it does
not happen with 'all devices'. It doesn't happen with my Android device, and it does happen with two other people I know of, who also use an Android device with their Autel controller.
Also, nothing electrical 'uses voltage'. Electrical devices use and consume
current, and voltage is the delivery agent for the current. (See Ohm's Law). I did a test with my android device and controller and found that there is NO current flowing from the Android device to the controller, or visa-versa. What does flow between the devices is DATA. Likewise, the data that is sent by the Android device is powered by the Android device. Inversely, the data that is sent by the Controller to the Android device is powered by the controller. Finally, each device is responsible for processing the data it receives from the other device. But, current is not transferred either way.
The possible reason that 'some' devices indicate that they need a charge is because THAT device has used, or is using, a depleting amount of current in order to do it's processing. The greatest consumer of current in either a tablet or a phone is the LCD screen. Additionally, simply processing video graphics also consumes more electricity (current). As a battery drops (is depleted of current), then it's voltage drops. An anomaly with a battery can also cause a device to report a 'low battery' (or need to recharge). One benefit of a lithium battery is that it's voltage (similar to pressure in a water pipe) remains consistent, even as current (similar to water in a tank) is depleted. Then, voltage avalanches when the battery (tank) finally runs out. When NiCad batteries were popular, they held more current (the tank was larger). BUT, as current (the water in the tank) was used, the voltage (similar to water pressure) proportionally dropped. If a Lithium battery has an anomaly, then voltage drops prematurely, which in turn causes the device to indicate a low battery.
Again, voltage is not consumed. Current (measured in Amps and milli-amps) is consumed. It is for that reason that the 'capacity' of a battery is measured in Milliamps or Milliamphours (how many milliamps can be delivered over a given period of time.)
Before technical advice is given, an understanding of the basis of that advice is necessary. By the way, if/when you get shocked, it's not the voltage that you feel; it's the current!