After plugging my phone in to a power source, it will not begin to charge the battery until I unlock it. My laptop similarly can “ignore” the voltage coming through the power cord.
How do these devices reject/ignore/disregard the voltage coming through the power cord?
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All modern devices include something called a “charger controller”. This is a little piece of circuitry that regulates when/how the battery is charged. This is really important with lithium batteries (i.e. almost all modern batteries) because overcharging them is a Bad Thing so you can’t just connect them straight to voltage, you need something actually actively controlling the charge process.
So when you plug in the power cord it’s not “ignoring” the voltage, the charge controller knows it’s there, but for whatever reason it’s decided not to actually start charging the battery until some other condition is met.
Many new phones & laptops are smart enough to recognize their usage patterns and optimize the battery charging cycle (start, stop, rate) to maximize battery performance. My phone, for example, “knows” that I’ll plug it in each night when I go to bed and unplug it when my alarm goes off. That’s way more hours than it needs to optimally charge the battery so, when I first plug it in, it’ll just say “OK, power’s here…I’m gonna wait a few hours then start charging”. It times it so that it finishes charging a half hour or so before my alarm goes off.
Likewise, my laptop is almost never off battery power, so I’ve got it set to maintain the battery at partial charge (extends the battery longevity). When I plug it in, if the charge controller sees that the battery is full enough, it just won’t charge it further.
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