I'm pretty sure many of us have heard at least one person tell us that leaving a phone plugged in when the power goes out will cause the battery to drain. While this saying has been popular for years, it isn't entirely true. Today, we are going to be confirming if this is truly possible or just another technological myth.

First, I'd like to point out that most smartphones today are made with lithium batteries and these batteries are very strict when it comes to charging and discharging.

Now that's cleared, We'll bring on the first factor of the of the whole charging process which is the charger itself. Most chargers collect very high frequencies of electricity from the plug point. This electricity then goes through the small transformer inbuilt in the chargers circuitry to convert it to a safe value which the device can handle and then travels through the cable and supplies it to the phone. In a case of power outage, The cable will prevent any power from flowing back into the charger circuits.



The second factor is the phone. Most smartphones today have built-in charge regulators. What these regulators do is that they prevent your phone from charging when it hits the 100% mark to avoid over-charging. Another thing they do is that, in the case of power outage while your device is still charging, It blocks the release of charge out from the battery through the ports back into the charger.

So you see, this is a two-way prevention technique to assure users a safer and stronger device and battery.

https://www.dailytechnet.com/discharging-while-plugged-in/

Ok

Educative

In other words, there's no such thing as battery 'discharging' when it's still plugged in without power.