[Android General] sky-head:
Executive Summary: Quick Charge, e.g. Qualcom Quickcharge 3.0 can be considered a very smart manufacturers' measure for built-in obsolescence and revenue maximization for the usage behavior of most smartphone users.

Preamble:

If you are used to buy one smartphone per year and this is nothing you worry about or consider wasteful or have a bad conscience about for environmental and/or child labor and/or wallet reasons, you can just ignore this topic, as it is not written for you. If you think that a smartphone should easily live like 5 years or more, as there is actually neither a software nor a hardware reason nor a style reason that ought to prohibit this - you might be interested in reading further.

How charging works and what Quick Charge does:

If I get it right, fast charge or ultra fast charge technologies, such as Qualcom Quickcharge 3.0, only use a higher charger voltage to increase the transfered power through the usb cable(!), while meeting the safety specs of all existing usb cables (and long-ago existing standards) that don't support currents of more than approximatly 2A (due to the small cable cross section and therefore high cable losses / heat / fire hazard danger). Transfering power at a higher voltage at the same current will generate the exact same losses (heat) but transfer more energy, as power is voltage times current. If I understand it correctly, the CC/CV-Charge-Cycle (CC = constant current; CV = constant voltage), which is common/standard for all lithium batteries, actually only supports charge voltages - directly at the battery input - of somewhat in between 3V and 4.3V (depending on the charge capacity state). It is actually not possible to directly supply the battery with a voltage higher than 4.3V (e.g. 20V, like a charger with Qualcom Quick Charge 3.0 could supply(!)) and using a reduced current instead (and therefore a reduced heat generation in the battery), because the current would just increase to very very very high values and the charging process might become highly instable and dangerous if such a high voltage was supplied directly to the battery.

This means basically:

Each smartphone must contain a step down converter (DC/DC-converter) that converts the charger voltage of something like 5V, 9V, 12V, or even 20V to a value between 3V and 4V during the CC-charge phase, while "converting the voltage difference" to a higher current, e.g. to 3A. The current generates the losses (heat) due to the (unfortunately existing) internal resistance of the battery (which is increasing as heat increases, increasing losses, increasing heat, increasing resistance, - a so called thermal walk-off, that's why the temperature is often measured during charging process - a vicious cycle). I just checked it for a Moto G5 Plus in Turbo Charge Mode: The USB power meter showed 9V and 1.45A (9*1.45=13W charge power at the output of the charger), being reduced to a value of about 3.9V on the internal lithium voltage input for the battery and a value of 2.8A for the charge current of the battery (according to the app "Ampere", which reads those values from the android system)!

Side note: This is a factual charge power of only 11W and the difference of 2W must be losses in the cable and of course the step down converter, which generate additional (unwanted) heat (or it must be a measurement error, which would be a little high for a measurement uncertainty, I think.).

For a 2800 mAh battery (2.8 Ah) it means that the battery is charged at "1C" (meaning that the capacity of 2.8Ah would be theoretically reached within 1 hour, if charging the phone with a constant current of 2.8A and a fully discharged phone at beginning of charging process). Unfortunately, it also means that a lot of heat is generated while charging and that the lifetime of the battery might be reduced dramatically - the hotter the battery gets - not as dramatic as for a "2C" or even "3C" charge, but a lot more dramatic than for a 0,33C charge, which would be only 0.9A for an 2.8Ah battery capacity. Lithium Battery life or aging, which basically means a deacrease of the original capacity, is extremly depending on

heat generation while charging (if you could keep your battery temperature regulated to like 15 degree Celsius by a cooling system as in car battery systems: it would be not damaged, even if charging at very high currents, as long as you are able to keep the temperature stable at 15 degrees Celsius. The heat is the factual problem, not the current itself.)

charge state (at how many percent of the battery's full capacity you store your battery... something between 50 and 70 percent is a lot more life preserving than 100 percent or 20 percent!)

But, guess what?:

There is neither an option for a battery life preserving charge state (e.g. keeping your battery on 60 percent) nor for a software limit of the charge current, e.g. by a simple app, because all of the charge features are extremly hidden and protected by the system. Even root does not provide control over it. I am not sure on this aspect and I am looking for an app that might let you limit charging current and let you redefine the fully-charged state, start of charge percentage, stop of charge percentage, etc. - so please feel free to correct me if I am wrong!. (unfortunately, I am probably not wrong...).

I can tell you one thing: Companies, such as Tesla, only use a very small range of their lithium batteries potential, as do all car manufacturers, as they could never ever provide a 10 year life time cycle for their battery technology if they'd use the same range as smartphones do (0-100 percent as reference). For a car manufacturer 0 percent means something like a factual charge state of 50 percent (speaking in smartphone terms) and 100 percent means something like a factual charge state of 80 percent (speaking in smartphone terms) - as they know that this will increase their battery life extremly. So they could actually make cars drive more than 2000 km (1243 miles) with one single charge, but they know that this would mean a bricket battery after one or two years, at maximum. Please don't pin me down on the exact numbers, but you should understand the concept. The second thing is cooling. Their batteries are charged in a way that you could not burn your fingers on when touching the battery, like it almost can happen on your smartphone, when turbo charge is running for like 20 minutes (my G5 Plus gets really hot, although "only" charging with "1C" - not even more).

Useful hint: If you use a magnetic car holder on one of your car's ventilation grids and use your airconditioning at a cold temperature in summer - you can save your smartphone's batteries life, especially when generating a lot of heat due to draining a lot of current (due to GPS navigation and display brightness at bright daylight) and parallel recharging with high current or similar... . But take care: In winter, when additionally blowing heat on your phone, the battery will die very early and you should fully close the ventilation grid, where the smartphone is placed.

The thing that makes me angry is not having control over it - for me personally - I would be perfectly ok with a charge state of 50 to 60 percent and an algorithm that only charges if the state drops below 50 percent and stops as soon as it reaches 60 percent. Also, I want a slow charge rate (e.g. 0.33C), which is only overruled if I want so - by hitting a button. Typically I go to work, I plug my smartphone to some charger. I come home, I plug my smartphone to a charger. I sit in the car, I plug my smartphone to a charger. I go to bed, I plug my phone to a charger. I am abroad, I plug my smartphone to my abroad charger in some hotel. Ocasionally - like five to ten times a year, I know (typically before) that I will need a full charge of a 100 percent as I will be out of charging possibilities for several hours and I will be needing something like GPS etc. In these rare cases I could easily switch the charge protection off by the hit of a button and the smartephone would be (maybe even quickly - if I whish so) charged to 100 percent. But it is just very stupid to take your almost discharged smartphone with a charge state of 20 percent, go to bed, plug it to a quick charger, let it charge to 100 percent within one or two hours, although you sleep like 6 to 8 hours. It is a total waste of battery life and there is abosolutely no reason for it. But why does none of the manufacturers give you control about charging? Do you get the message? They profit. They profit from early bricket batteries, as it is the most common reason for users to overcome their old phone for the sake of a new one - mostly accompanied with a lie to themselves like "Changing my old (built-in) battery would cost alnmost as much as a new smartphone and then the smartphone would still be over a year old, which is really old - so I am just going to buy a new one. Besides, hitting one-click on amazon is a lot less trouble than having to find the right battery and someone to replace it. I will better dump my old smartphone." (and generate enormous amounts of electronic waste that mostly gets illegally dumped somewhere in Africa, where children try to burn the phones and get one or two grams of precious metal out of it, while breathing toxic gases).

Why would Smartphone manufacturers or Smartphone CPU-manufacturers, such as Qualcom, want that?

Another - probably true - story, or call it conspiracy theory: I can really really imagine as some business guys from some smartphone company where sitting together with their techies. The techies told the business guys: "We can unfortunately not charge at higher currents, making the batteries die more early, because the usb standard forbids it and existing cables might catch fire. It would be too risky. All other planned obsolescence measures would be highly illegal - you know what happend to Volkswagen or Apple, do you?". [You could also imagine the guys from Qualcom asking: "How could we make Smartphone manfacturers sell more Smartphones and us supplying more CPUs...?"] The business guys groaning in a desperate mood: "What can we do to make them buy ... more smartphones ... more often ... we must... find... something" - until one techie suddenly came up with the idea "we could increase the voltage to break those stupid existing usb standards as we only have to keep the current as low as 2 amperes to prevent the cables from burning!". "Then we could transfer a lot more energy to the smartphone, where we use our built-in heat generators to make the batteries get very hot during charging, making them die very early, making customers have to buy more phones, more often! And it doesen't matter how we generate heat, all losses will generate heat. No matter, if in the battery or in the step down converter - that's awesome!". That techie got a reward of 5.000$ and some clammy handshakes for his idea, while the business guys live in the Caribbean now, in their palaces. And the worst thing about it is: Everyone is happy, including the majority of uninformed customers that think they were blessed with this terrific new Quick Charge feature. That's what I call a really really smart measure of built-in obsolescence! Just waiting for the first manufacturers to offer 2C- or 3C-charging - it will come soon - and customers will be beaming with joy, while watching their battery charge state increase percent by percent each ten seconds.

To put it in a nutshell you could basically consider the quick charging feature just as a planned obsolescence measure to make customers buy new smartphons even more often(!) than they already do, as their (nowadays, of course) built-in battery will die a lot earlier and cost a lot of money to be replaced by an original one, making the decision to buy a new phone look more convenient. The primary manufacturer interest is making you buy more smartphones, more often and increase their - anyway enormous - revenues. Other manufacturers' techies (of course) realize that quick charging technology will basically age batteries 20 percent earlier - but even if they wanted therefore not to adapt the quick charge concept, they would lose customers, as the average customer is unfortunately not very smart or technophile and will only be able to draw relativly stupid conclusions, such as: faster charging = better smartphone; slower charging = inferior smartphone. "Must buy faster charging smartphone!"

Other thoughts:

No, no, definitely no - it is not an considerable option to control the charge process manually and keep the charge state within the range of 50 to 60 percent manually. It is also not an option to have to buy multiple chargers and keep one quick charger and one oldschool charger at every place you want to have a charger, just to make sure that you can use quick or slow charge, when you need it. This is totally inacceptable as it could be solved by software easily!

At least my G5 Plus seems "only" to charge at 1C, which is a lot less worse than 2C or 3C charging. Still, 0.33C charging or less - especially in combination with keeping your battery between 50 and 60 percent of capacity most of the time - would probably increase battery lifetime in a way that the battery could remain in the almost exact same state as a brand new battery, even after a period of five years. At least if you'd also take care about not overheating your phone's battery (e.g. leaving your phone in the car in summer or leaving it in direct sunlight, while lying at the beach for hours!). Another battery killer is of course discharging by drawing massive amounts of energy, e.g. GPSnav+Teethering+BrightestDisplaySetting+PlasticCoverThatKeepsHeatInTheBattery at the same time. Probably, this could be even more battery life killing as 1C charging.

As it is not the current itself that ages the battery but the heat it creates - one should consider things like removing your plastic protective case, which is typically a thermal insulator and will keep a lot more heat in the battery during charging, avoiding heat conductive cooling. Probably the best thing would be to blow cold air on your phone, especially while high speed charging (e.g. magnetic car holder at the ventilation grid in combination with air con in the car.) or at least placeing your phone - without cover - on some thermally highly conductive material, e.g. a metal plate (like on a stainless steel pot base...). This will suck the heat from the battery very quickly and therefore do less harm to the lithium chemistry. I can imagine that some companies might eventually offer charger combinations that do something like 3C-charging, while your smartphone is being cooled by some Peltier-elements, with an incredible charge speed for a full charge of something like 20 minutes, without harming your battery too much. But it is a niche with regard to the fast moving smartphone market.

What do you guys think?

PS: The topic might be better in Android General - but I am not sure... I would be very interested in an app, as explained in the text. But it is actually a more general topic.