By Wakoli Kunani
Does Charging a phone for a long time damage the battery?
Answer by Dave Haynie, Electrical Engineer.
“Not even remotely.”
When you have your phone plugged in, that thing everyone calls a “charger” is just a power supply, like a battery or other DC adapter. The charger is part of the phone’s power management circuitry.
When you plug power into your phone, the power management circuitry will first use that to power the phone. It has to, because a battery can’t be simultaneously charged and discharged. So assuming the phone doesn’t suck up all the power, the phone’s charging circuit will start charging the battery.
The charging process keeps going until the battery is full. At that point, the charging circuit simply stops charging the battery. Your phone continues to run from the power input. If there are any power surges that can’t be handled by your wall wart, most phones can combine power from the power input and the battery. But if the phone’s just still idle, most power dongles will easily power the whole phone.
The phone’s power management circuitry is still monitoring the battery. If that charge should drop below around 95%, the charging circuit will top it off again.
This is actually how all USB powered systems work, since the USB power dongle isn’t a charger, just a power supply. This allows your phone to perfectly run the charging cycle needed by its battery without concern about who’s supplying the power. And it even allows different battery chemistries to be charged from the same “universal” plug.
As others have mentioned, it’s not recommended that a phone battery be stored long term under power. Batteries at full charge or near zero charge wear out a bit faster than if stored half-full. They also wear out faster if stored in a hot environment. If you’re storing a battery for a month or more, it’s best to put it away with maybe 60% charge, but enough to account for about 3% self-discharge per month. In normal use, most chargers switch off once a battery reaches 100%. Some will kick back in once the battery drops to 95% or so, others require some kind of reset to turn back on again.
I am trying to differentiate normal use from “damage.” Technically, any time you charge your battery, some of its useful life is used up, so technically that’s “damage,” and yet, not using the battery at all is a pretty useless application. So of course you’re going to use it, and most users need their phone at 100% or close to it every morning. If you want the absolute longest battery life, keep it between 20% and 80% charge or so… that’s what hybrid cars do to make their batteries last indefinitely.
My point here is that modern devices do not suffer from any sort of damage due to overcharging to a battery left charging.