Now that you mention it, the day I started getting bad battery life was the day after I let the phone discharge to 5%. But, I did a full night charge while off and my phone started getting the best battery life as before then I did another full night charge while off and the bad battery life returned. I was hitting 50% at 3 hours of screen time whereas before it would hit 50 at 4-4:15 hours.
Not everything in battery life is related to screen time. Yes, screen time is generally the biggest battery hog, but not always. There are LOTS of factors that can influence the overall battery endurance and create what is perceived to be poor performance. Varying levels of signal is one that is easily overlooked and quite often is the single biggest variable in battery endurance.
Look at your battery performance chart, tap the chart and look below the chart to see the signal levels. They will show up in varying shades of Yellow to Green, like this one...
View attachment 60911
You'll also see other lesser obvious stats such as GPS, WIFI, Awake time, Screen on and Charging periods. This lets you see how each affected the discharge rates more directly by looking above at the slope immediately adjacent to the various indicators.
For instance, the chart above shows six obvious and relatively steep slopes;
- immediately off charge,
- 1/4 in,
- 1/2 in (*2 drops...the 1st drop),
- 1/2 in (*2nd drop),
- 3/4 in and
- 4/5 in,
...all which correspond with 4 concurrent events...low signal level, WIFI on, Awake, and Screen on as seen in the short Blue sections in the bottom two bar charts. There were actually a couple more less obvious dips that corresponded to shorter bursts of Awake and Screen on, giving me an obvious understanding of 8 more rapid power declines, which when added together resulted in 25% of the total available battery being consumed (i.e. from 100% to 75%), or 71% of the 35% total (100% to 65%), battery power actually consumed (25% / 35%). Those short bursts were only 35% (4 hours), of the total time the phone was under battery power (11.3 hours), meaning that 65% of the time the phone was sipping power very slowly, over 7.5 hours of the 11.3 hours, so you can see how those short, high demand periods can dramatically diminish the battery's endurance.
These batteries are quite capable of putting out very high current for relatively short periods of time, but where they shine is in putting out very low current levels for extensive periods of time. In other words, you will get exponentially far more time out of one charge by consuming the power slowly (with the phone in rest state as the best example), rather than consuming rapidly (such as while streaming video through 4G).
