I agree with the concept of recalibrating the charging system to the battery's real and likely diminished capacity due to its aging. Because of the way these Lithium Ion batteries charge and discharge, and how they lose capacity (maximum mAh they can hold in one charge), over time, the charging system needs to see "reference points" of what a charged and discharged battery looks like (voltage levels), A battery that's between 1-2 years old can actually be reduced in maximum capacity by as much as 20%, meaning that it will now only hold 80% of its originally rated mAh capacity. This is completely normal however getting 2 years rather than one is more consistent with normal.
By recalibrating the charging and metering system, the phone can then can better determine the battery's State Of Charge (SOC), during the future discharge cycles and readings of % remaining will be more accurate. However I recommend avoiding allowing the phone to get below about 10% battery levels, and almost never except under the most extreme situations where it is absolute necessity to use (such as in an emergency) should a phone be used approaching or allowed to shut down with 0%. The reasons are numerous but the main ones are;
- Lithium Ion batteries do not "like" to be either in the top 20% or the bottom 20% of the charge range, and much prefer to be kept in the 30% to 70% range for maximum longevity (life of the battery, not life of the charge). By charging before the battery gets in the 20-30% range, and using your charger more as a boost charger rather than a long-time "overnight" charger will extend your battery's life considerably. In some cases this can extend battery life by actual years.
- Lithium Ion batteries self-discharge and at the same time are at risk of going into "protection mode" automatically if the battery's voltage dips too low. By shutting down at 0%, rather than "dying" (like older appliances with batteries such as those with motors where they would simply slow down and eventually stop), it leaves a minimum voltage level (about 2.7-3V), in the battery to "protect" the battery from going into a self-destruct state where it could result in overheating and bursting into flame.
If the phone's metering system is out of calibration it can actually allow the battery's voltages to dip lower than the minimums and the battery can fall into "protection mode". Once in "protection mode" the battery will be unresponsive to most normal charging attempts, however can be shocked (boosted), back into normal charging range with several techniques and expensive charging station equipment. In some cases you can boost it back into normal charging range with a modified cable to connect directly to the battery but that's dangerous and should be avoided if possible.
- In some phones, most notably the Motorolas (but can affect all Lithium Ion Battery phones), if the battery dips below 0% the phone can become completely non-responsive to a charger or the power button, and in many models will display a "white" LED (known as the "White Light of Death"). This is where the battery will not take a charge since it's below the minimum charging range threshold (apporaching but not yet at protection mode), and in many cases the battery is rendered completely useless and must be replaced.
Those who are highly technically inclined and who's phone is likely recalibrated far more than most may have had much success with discharging to an unresponsive phone, however I would not recommend the average user to subscribe to those practices. Forcing to "calibration" by making sure the phone stops turning on is something I would NEVER recommend to cell phone users, and most specifically to Motorola phone users, however this may also be much less of a problem with Samsung phones. If their meter is so far out of whack that it's reading 7% when in fact it should have shut down several minutes ago, you could be dipping close to the minimum "protection mode" voltages.
I say use your battery meter like you use your car's gas gauge. You would likely never let your car run until it stalls and won't start again. When the "empty" light on your dashboard lights, it's an indication that you are "nearing" empty, (there's a reserve area in the tank that holds about 1-2 gallons for that purpose), and it's a warning to get to a gas station pronto. The same purpose was engineered into the phone. When it says "Connect to a charger", there is between 10 and 15% remaining charge - a "reserve tank", and it's for good reason. It doesn't want the phone's battery to be depleted to 0% and risk protection mode. Another reason is that on the chance you should need to use the phone for an emergency, it would be dead, and you may be too...
In my understanding, forcing calibration is done by hitting 100% with power off, then draining to the recharge indicator, followed by hitting 100% again with power off. That full, empty, full process is all that is needed and is what triggers the two reference points or flags as it were.
On a side-note, however I had miserable battery life with the S4 for the short 3 months I owned one and is the main reason why I traded it in for a Droid MAXX. Back to subject...
By doing a 100% charge with POWER OFF, followed by a normal day's use till the phone tells you to recharge, then followed by another 100% charge with POWER OFF, you'll set the reference points for the charging and metering system and the battery and phone should perform normally from there forward. This practice of "meter training" should be performed about ever 2-3 months under normal use, or once every quarter for simplicity.
Also, the idea of unplugging at the end of the charge, and then plugging in again to "make sure it is at 100% (called "bump charging"), is actually bad for the battery. The charging circuit knows when the battery has reached its rated capacity (*or it's now diminished capacity*), and will shut off charging automatically to prevent the battery from creating internal "shunts" (metallic shorts), which can cause thermal runaway and can result in a battery becoming unstable and risk a fire. By "bump charging", you are essentially trying to force more power into the battery than it's capable of safely storing, thereby putting the battery into a voltage range beyond its safe capacity. This should be avoided.
It's natural for a Lithium Ion battery to shut off charging at 100%, and then be sitting there connected but not charging until you remove it (like when charging overnight and then removing it at daybreak), and come to find that it's reading less than 100%. Truth is it has likely not really lost any appreciable level of charge, but instead what happens once a rechargeable battery is removed from charge at its highest voltage level (a key indicator of the end of charge), is it will then begin to "relax", where the voltage will trail off slightly as the battery cools down and internal electrochemical processes come to a balanced state.
If you check the voltage of a battery at full charge immediately after charging and then check the same battery in as short as an hour later or less, you will typically get a lower voltage reading at the second test even if the battery is completely disconnected from any device and just sitting on the bench. Again, when you pick up that phone after charging overnight and you see the battery level at let's say, 95%, don't be alarmed that the phone has "used" 5% of power, or that the battery didn't take a "full charge". This is completely normal and shouldn't prompt anyone to "bump charge" the battery.
Now, we've gone off-topic slightly here, and I've definitely gone down that vein a good bit farther so I'll try to wrangle this back to where it was. The OP
@curious_george was complaining about excessive battery drain, but with no obvious causes. The more recent complaint is from
@adrenalnjunky a situation where the Android OS has apparently gone rogue and is sucking down an inordinate amount of power, the phone is getting warm, and this is mostly attributed to times when the phone isn't even being used. These symptoms are typically results of apps or OS getting off track and not as a result of a battery metering system that has slipped out of sync with the battery.
I would concentrate on identifying what application or applications, services or other OS issues are causing the phone to "stay awake" and heat up while resting. Also not mentioned, his could be at least partially due to low signal level as well, something that affects lots of us and we bang our heads on the wall trying to identify the real causes. I have proven on many occasion where my battery is depleting quickly and how it corresponds to signal level on graphs. It pays to see the second graph behind the main one at the top in Battery Stats. To show that graph, tap on the graph at the top and it will show the battery graph again but this time it also shows several additional key indicators, such as relative signal level, awake time, screen time, etc., all in a graphic format and chronologically in sync to see better what may be causing excessive battery drain.
