What's wrong with my phone?
I tried my best to make sure that I do not overly drain my battery too much before charging to reduce stress on it. After a while, I realised that my battery meter seems to decrease really fast from 100% but lasts disproportionately longer from 20% and below. This was a sign that the battery meter might be out-of-sync with the battery. Let me explain.
Typically, battery meters on digital devices such as laptops and phones are only estimates. Other than the determinable points such as the "full charged voltage" (100%) and "critically low voltage" (point where phone shuts off), it is very difficult to determine how much charge a lithium-ion/polymer battery has left between those two determinable points. Why? Lithium based batteries often hold their voltage very well until depletion and thus, making it very difficult to obtain a good estimate of the charge level by taking reference from the battery voltage.
As such, battery meters measure the amount of charge going into and out of the battery during charging and usage to estimate the remaining charge in the battery. Over time, the meter can get out of calibration due to random error due to things like difference in temperature, increase in battery resistance due to aging, battery self-discharge, etc.
Honestly, I forgot about battery calibration until I accidentally drained my phone battery till it shut off as I did not have access to a wall socket for 2 full days.
I was on the bus and minutes away from the safe refugee of my charger before the my phone decided that it was enough and shut off on its own at 2%.
How to recalibrate your battery meter:
I took the chance to recalibrate the meter by simply leaving it to charge for about 2.5 hours without unplugging it or using it. I purposely left it plugged in longer than I know it takes to obtain a full charge because I had to ensure that the battery had really reached its "full voltage". Remember, your battery meter may not be accurate even though it shows a 100%. However, the charging electronics will be able to tell if it has reached full charge and terminate charging.
After that, my phone was able to last 1 full day without charging compared to half day. Not bad considering that the battery had spent 2/3 of its expected lifespan.
Afterthoughts:
IT equipment has become so advanced to the point where everything is so convenient to the user. Gone were the days when instruction manuals were thick and explained the workings of certain user-maintainable components. Manufacturers expect their products to work perfectly for the user without the hassle of having him/her learn how to use it, which is why everything is so simplified and obscure to the user.
You may have encountered cameras with simplistic bar battery meters which deplete very quickly after losing the 1st bar. This type of battery meter attempts to use battery voltage as a reference, but is pretty much useless because it is rather drastic. Below is an approximation of the battery charge compared to typical battery indicator icons.
