why most electronic devices perform worse and worse as the battery life shortens? shoudln’t they always perform at peek as long as there is battery?
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Examples: flashlights, laptops, toothbrush, etc.
As a battery gets older or as it gets lower charge the amount of power it can provide at once is also lowered.
More complex devices, such as laptops or smartphones can adjust their processors and other components to try II and handle this, but it can mean somewhat reduced performance for high demand tasks. If you’re just reading an email or posting on Reddit you might not notice, but try doing a more demanding task like render a 4K video and you’ll see a slowdown.
For simpler devices like flashlights or toothbrushes you’ll notice more directly.
Imagine you’ve got a tank of water, and you poke a hole in the side near the bottom. At the start,the water comes out of the hole really quick, because there is the pressure of all the water above it. As time goes on, there is less water above the hole, meaning less pressure, so the water comes out slower and slower, down to a dribble. Eventually, there is no water above the hole so the flow stops.
This is a simplified metaphor, and it more directly describes a capacitor than a battery, but the principal of “the closer you are to empty, the lessbyou can pull out at once” applies still to batteries. And springs and flywheels and pressure tanks and heat storage. Lots of energy storage devices really.
For analog devices, like the ones you listed, their components are designed to work at around a specific voltage. As batteries deplete, the voltage they can sustain drops as well, making the bulbs, motors, etc perform worse than they should.
Thanks all for the great responses. Basically lower charge = lower voltage throughput
Batteries are not like power plants that provide a consistent 110 Volts to your house. Batteries produce their electricity (voltage and current) from a chemical reaction, and as the battery ages that reaction goes slower, so the voltage and the current from the battery decrease. So your device gets less electricity to work with.
It’s like trying to generate electricity by [pedaling](https://kicanada.com/resources/image/18/7f/c.jpg), when you get tired there’s less electricity.
Battery voltage drops during discharge. For most “analog” devices like electric motors or incandescent light bulbs their output (rotational speed, brightness) depends directly on voltage. So if a Li-Ion battery drops from 4.2V to 3.3V you’ll see roughly a 25% change in output performance.
Battery voltage also drops the greater the load (current) is. This is called internal resistance. Older batteries in bad shape have a higher internal resistance which makes their voltages drop further. Internal resistance gives an upper limit for the power you can get out of a battery. If you put a thick wire between the two poles of a car battery (low internal resistance, a few mΩ) it will simply melt the wire. If you do the same with a measly AA alkaline battery or coin cell (~1Ω and ~20Ω internal resistance respectively) the wire will merely get slightly hot.¹
Devices with more complex electronics usually have a voltage converter in them which converts the battery voltage to a fixed voltage. For example from 3.3V – 4.2V battery voltage to a constant 5V. These devices shouldn’t see any change in performance when you discharge them. However, If the battery is very old and its internal resistance high the voltage can drop below what’s healthy (or even sufficient to power the device). That’s why Apple had to limit CPU performance on some older iPhones.
¹: Related fact: With LEDs you usually need a dedicated series resistor to limit current. However, when you open one of those tiny coin cell LED flash lights you’ll often only find a LED directly connected to the coin cell battery. Looks crazy at first when you’ve been taught that you *always* need a series resistor for LEDs. Until you realize that the high internal resistance of the battery acts like one.
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