What is it about electricity which causes this? Why can’t a device draw full power until the battery is dead?
In: Physics
Imagine a simple electronic device like a bottle of water with a hole at the bottom side.
When the bottle is full the water flows out at high speed, and can turn a water wheel quickly.
When the level in the bottle is lower the water comes out slower and the water wheel turns slower.
That’s exactly what happens in a simple electronic device: the battery when going empty has less ‚pressure‘ or correctly voltage to ‚push‘ the electrons out.
In a more complicated device there‘s electronic components in there, the can step up the voltage but with less electrons flowing.
In the bottle and water wheel example above: you attach gears to the water wheel to make a second wheel spin faster despite the main wheel having slowed down.
However while the second wheel does spin faster, it‘s very easy to stop by just grabbing it, which the water wheel wouldn’t be.
So something like a smartphone or a laptop has electronic components that turn the voltage of the battery that eventually stops down to a constant voltage. The device only turns off once the flow of electrons isn‘t high enough anymore.
Either way: when the battery is nearly empty, even when you step up the voltage you always reduce the flow of electrons.
Because the voltage and the current are directly linked.
At a specific ‚emptiness‘ voltage multiplied with current is constant.
So doubling the voltage halves the current.
And the phone or laptop has a minimum current it needs to light up the display and keep basic functions running.
When either the current or voltage were to drop too low the display wouldn’t be visible anymore and the cpu would crash.
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