Some questions above smartphones' batteries

[Android Central Question]

Hello. I have some questions regarding smartphones' batteries. Any answers would be appreciated:
1) I have a Xiaomi Redmi Note 5 Pro smartphone that has a 4000 mAh Li-Po battery. When I bought it, the seller explained to me that in order to keep the battery good for long, when the battery gets to 20% I should charge it to 80% and so on every day and only once a month to let it drain to 0% and then charge it to 100%. My question is- is this really the best way to keep Li-Po batteries alive for a long term? If not, what is?
2) I read once that when updating the phone's OS, I need to drain the battery to 0% and then charge it to 100% so the OS "learns" the battery capacity and the battery "knows"/"remembers" it has 0% to 100% and so I've been doing so every time I updated the phone's OS. Is this a correct thing to do or not?
3) Lately I've upgraded my phone's OS to MIUI (Xiaomi's android based OS) from MIUI 10.x.x.x to MIUI 11, so I've tried draining the battery to 0% and charge it to 100%, as mentioned... The problem is, the battery doesn't seem to "know" the last few percentages before 0... I mean, one time it turned off at like 7% as if it was 0%, so I turned it back on, drained it to 0% fully and then recharged to 100% and now again it turned off at 2% instead of 0% AND when I plugged it to the charger, it starts charging from 8% even though a second ago it showed it was at 2%... Why is that happening? Does my battery not "know" the last few percentages? Is it normal? Should I indeed drain it to 0% completely and then to 100% etc, as mentioned above?
I hope to get some professional answer to these questions, which will help all Li-Po batteries users who'll read this thread.
I have this smartphone for 2 years now. Thought to mention it, if relevant.
Thanks in advance for answers!!

 

[hallux]

This should get you started - https://forums.androidcentral.com/a...e-care-feeding-lithium-polymer-batteries.html

I have never drained a battery to 0 after an OS update, it's actually bad to do that with a Li-Po battery.

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[mustang7757]

Phone manufacturer give a 1 -3 year window how long a battery going to last . Manufacturer only give 1 year warranty on their battery . Independent research labs found 40 to 80 is best , I personally do 10 to 95 or 100 without issues. Main thing to avoid is having the battery depleted often , extreme temperatures and playing lot of intensive games. Once you go to 5 percent to 95 this method recalibrate the battery but doesn't need often, Plus you need to reach 90 to reset battery statistic in phones built in battery monitor. If you have further questions can register here to communicate,as a guest account you can't.https://forums.androidcentral.com/showthread.php?t=409154

 

[Mooncatt]

The thread @hallux linked to is a great starting point, and includes links to the experts at Battery University (who do lots of controlled testing). To elaborate a bit on your questions:

1. Yes, the seller is correct if you're goal is the best overall lifespan, but 20% is cutting it close. Maintaining 40-80% is a more common suggestion. The key is Li-ion batteries like a happy medium.

2. I've never heard that and have never ran a 0-100% calibration charge after an OS update.

3. The battery meter becomes less accurate at those low percentages, so that may be part of the early shutdown. It's more likely that it's the beginning signs of the battery wearing out. Without getting too technical, it's related to voltage sag. Any time a load is placed on a battery, the voltage drops. On a healthy battery, this isn't an issue. As it ages and the internal resistance builds up, the voltage sag gets worse. When it drops below the cutoff point, it's an instant shutoff before the meter has a chance to notice and update. That's why you see it shutoff with an apparent 5% left. It's not uncommon for this to keep getting worse, and I've seen some people get bad enough that it shuts off with 25% remaining.

 

[Rukbat]

Hello. I have some questions regarding smartphones' batteries. Any answers would be appreciated:

(My effort and study in the article hallux linked to, so):

1) the seller explained to me that in order to keep the battery good for long, when the battery gets to 20% I should charge it to 80%

NO, NO, twice no! NEVER let it drop below 40%. 50% is an even better charge point (it keeps the battery living longer), but at 40%, if you can't charge it, TURN THE PHONE OFF!

and so on every day and only once a month to let it drain to 0%

NEVER!!! Never let it drain lower than 40%. (If you want to keep the battery lasting longer. If you want to make the seller happy, drain it to 0 every month - he gets paid to replace the battery you kill by doing that.)

2) I read once that when updating the phone's OS, I need to drain the battery to 0% and then charge it to 100% so the OS "learns" the battery capacity and the battery "knows"/"remembers" it has 0% to 100% and so I've been doing so every time I updated the phone's OS. Is this a correct thing to do or not?

Again, NO! The phone doesn't "learn" anything about the battery*.

3) Lately I've upgraded my phone's OS to MIUI (Xiaomi's android based OS) from MIUI 10.x.x.x to MIUI 11, so I've tried draining the battery to 0% and charge it to 100%, as mentioned... The problem is, the battery doesn't seem to "know" the last few percentages before 0... I mean, one time it turned off at like 7% as if it was 0%, so I turned it back on, drained it to 0% fully and then recharged to 100% and now again it turned off at 2% instead of 0% AND when I plugged it to the charger, it starts charging from 8% even though a second ago it showed it was at 2%... Why is that happening?

1. It sounds as if the battery is developing a dendrite down below 10%, (It's why the auto industry is still spending billions trying to develop a lithium battery that doesn't develop dendrites. Electric car batteries are covered by the warranty, and replacing one every year for the 5 or 10 year warranty will cost the car manufacturer more than you paid for the car. But ... since you're never going to let a lithium battery drain below 40% ever again (right?), that's not a problem.

2. You've probably already harmed the battery a little, but I wouldn't worry about it. Just start charging it at 45% or 50%.

As for not charging it above 80%, only if the phone is already very hot (like sitting in a hot car in the summer) - but you should never do that anyway. Once the battery reaches 100% (and the phone knows it - *the battery's terminal voltage, which is what the phone measures to tell you "how charged" the battery is, stops rising), the charger (that's a chip on the motherboard - the thing you plug into the wall is just a power supply) shuts off.

But ... if it should ever fail, and keep charging the battery, you can cook the battery to death. So either disconnect the charger as soon as it gets to "100%" (which is actually about 99%, due to the fact that the terminal voltage includes the charger voltage), or use an app like GSam Battery Monitor and set the alarm to 99% or, if the phone is rooted, install Battery Charge Limit and set it to stop at 99%. (My Note 3 battery started bulging after about 5 years, so I replaced it. But I still keep the bulged battery charged to about 50% (that's how you store a lithium battery for long term). It's down to about 98% capacity now. After over 5 years of daily use. (But the back cover no longer fits because it's bulged, and it could burst, so I'd only use it in an emergency.)

But my V-551 battery is still good - and it's 15 years old. The only problem is that the V-551 can't be used any more because AT&T no longer uses 2G for voice and text. But there's no reason to have to replace the battery until you get so tired of the phone you don't care, it's lacking in so many features that you want to replace it (my Note 3 still works fine - but no fingerprint sensor, which I needed) ... or the technology moves on and the phone can no longer be used. The "batteries only last a year or two" stuff is nonsense.