Wait leaving your phone on the charger all night is bad for it? Doesn't the charging circuit protect the battery?
Well... battery protection circuitry protects your battery from overcharging and going all explody on you. When you leave a fully charged phone on a charger, what ends up happening is that it goes through a bunch of microcycles. It reaches full charge, but since your phone is still on (known as a parasitic load), it'll draw a little bit of power and then it'll charge back to full again... it does this over and over. It would be awesome if phones had power systems designed to completely bypass the battery when it hits 100% and have the phone run straight off of the wall current. But they don't.... you are running off the battery the entire time, it just throttles the charge rate to match.
Now, also keep in mind that the 'stress' a cell is under will increase as it nears its saturation voltage (full charge) as well as when it nears full depletion. How much stress is a function of how much charge you are pushing into it. That's why all phones will slow down charging as it nears 100%... Those recommendations to not charge past 80% are based on this concept. Under 80% (and over 30 or 40%) charge stress is minimal. That's why all those fast charge systems only truly fast charge in that meaty portion where the battery can take a ton of juice without breaking a sweat. If they kept charging at those fast charge speeds straight to 100%... you'd probably be able to use the thing as a space heater for a bit until it failed and decided to breathe fire.
A lithium ion based battery, if it lives its life between this lower and upper limit will last a very long time, certainly longer than what you would consider to be the current usable lifespan of a phone... which, sadly, is still not really that much longer than 3 or so years... at which point it the software will be grossly out of date.
So if the phone is left on your nightstand overnight, it's pretty much under charge stress for most of the time. It's not a ton of stress, but its still stress. Over time, this all starts to add up and the speed at which the battery degrades increases.
It's this same reason why it's not that good for the battery if you keep a fully charged phone on the charger and start using a power intensive application, like a game. Rather than the slow discharging of a sleeping phone on a nightstand, you are drawing significantly more power and forcing the phone to charge back up to 100% at a much higher rate. So if you are on the road a lot and tend to leave it plugged in while you are using a navigation app like Waze or Google Maps, you are putting a substantial strain on the battery. You'd be better served unplugging it and letting it drain.
Anyone here have a laptop that is left plugged in all the time? If so, I am sure you are well acquainted with having a battery be completely toast. Laptop batteries are exactly the same kind of cells, just more of them. And that laptop draws far more power... an always plugged in laptop can kill a battery in as little as 6 months. Some laptops actually have smart charging profiles that artificially hold the charge to 50 or 60% and allow you to set a time where you might want it to have it fully charged.
Sorry for the tangent... but coming back.... keeping it between 40 and 80 isn't exactly practical for the most part. So there are some other real-world practices that you can do that will strike a good compromise:
- Avoid leaving a fully charged phone on a charger for extended periods as best as you can
- Don't make a habit of draining it below 20% and certainly to the point where the phone turns off.
And, lastly, the Pixel 2 XL has excellent battery life, so don't stress if you have to head out and your phone's not fully charged. This phone has more or less cured me of battery anxiety. I no longer keep a arsenal of battery monitoring applications running, nor do I obsess over the little battery meter up there in the top right. I know the thing is going to get me through most days with ease.
Do those three things, and chances are you will have got rid of the phone before the point where the battery has degraded significantly enough to have become a nuisance.