Android smartphone battery suddenly drained twice as fast than usual
Next day, seems that all works fine again, apparently due to one of these two simple actions (but I don't know which one, or both, are the real remedy!):


Just after the most recent charge I temporarily (see below) turned the device into Economy mode (using Settings > Battery | Top right menu > Economy mode).
Having looked at several related questions here in AE, I wanted to try clearing the system cache, but inadvertently missed the double press power+volume so I ended merely turning the device off then on, instead of processing clear cache; then I gave up for the moment.


The unexpected (but fortunate!) result was that the battery level remained > 90% during the next 12 hours, so I decided to deactivate the Economy mode and wait to see what happens.

Now, about 24 hours later, the battery level is still 62%, and the chart shows a prevision of 4 days availability before to be empty: four times better than when I noticed the issue, and even twice better than it used before the issue appears!



EDIT: 10 days later, I can confirm that the improvement is real and persists. But there is more.

A very interesting (although unexplained!) point is that not only the battery stopped emptying in less than a day, but now it takes about 4-5 days before reaching 10%: in other words now the battery life cycle is more than 2x better than ever since I got the device!