Wow. Can you be more specific? Lol
Great question and observation. I've tackled this very issue of differences between power tools and phones in the past, but the short of it is they both draw current at very different rates (when's the last time you drilled with your power tool for 25 straight hours, non-stop?), and the two battery types are actually significantly different in chemistry. One is designed to provide high current in short bursts of relatively similar current levels (drill), the other is designed for low current draw over extended periods of time and at comparatively widely varying current levels (phone).
Simply by the way power is consumed in the drill, it's very easy for the tool to know when the battery needs to be charged... As it nears being depleted, the high current draws start depressing the voltage, the drill begins to slow and lose torque, and the voltage drops precipitously. Those significant changes in voltage are very easy to detect and the result is the monitoring circuit says "were near the end, shut down now to protect the battery."
In contrast, a phone's current draws are mostly very low and the battery can easily keep up with the demand for current without suffering voltage drop, even when near the critical low voltages where the power tool would have long since given up completely. Since the voltage doesn't drop in a pattern that is easily discernible, the metering circuitry has a much harder time determining when to call it quits.
Furthermore, you don't likely have a power meter on your power tool that tells you in 10% (or for that matter 1%), increments how long you have until charge is needed. If your power tool dies in the middle of a job, you pull another off the charger, slap it on and continue where you left off. However if your phone battery dies, it could be life threatening or financially devastating, such as not being able to make a call to 911, our losing your connection to the client you were trying to persuade to do business with you. In other words, the phone is far more mission critical, so the battery must be able to stand tough for those marathon sessions and still deliver.
So the phone's meter needs to not only accurately know what the full charge and depleted charge looks like, but also calculate where along the path to depletion it is at any given time, through a very long and gradual voltage depletion phase, and make sure it doesn't get too deeply depleted least it trigger the battery's protection mode...a very tough job. Add to that, the fact that one high current draw due to perhaps streaming a movie in a poor cellular coverage area could depress the voltage low enough even when sufficient current remains, to essentially "fool" the meter into thinking the battery is dead and trigger a shut-down.
Over time as it "sees" these voltage dips and interprets them as a depleted battery, it then uses those artificially depleted voltages as the "new low". There have been many cases where the phone says the battery is depleted but the phone remains running for hours past when it should have shut off if the meter were accurately gauging the remaining power. The inverse is when phones report there's 40% remaining, then only minutes later shut down without warning and become unresponsive to the charger.
There's lots more to it than this but to hopefully keep from boring nearly everyone to sleep I'm trying to condense it.
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