Confused about discharging to 20% and charging to only 80%. Read often that Li-Ion batteries must be discharged fully and charged fully to maintain their capacities. Which is correct?

So basically don't use your batteries in a way that's convenient for you? This is like the people who have to change their names to fit computerized forms.

One of the things I wonder about here is what "0%" and "100%" actually mean when most battery charging is controlled by complex management circuits, and levels are displayed by a piece of software that recalibrates itself on an ongoing basis. Are our phones actually charging to 100% of their electrochemical capacity, or just to 100% of the 80% that their software considers the upper limit for longer life? Same on the bottom side: it's pretty clear that "0%" isn't actually empty, because a phone or other device typically still has enough juice to display a message saying it has no power left...

(A family member had a phone that wouldn't charge above "30%" as indicated on the display, even though battery life indicated a much higher level. The phone died before the promised software update to display the "right" number.)

Interesting article but hope that they don't use lithium-ion batteries in electric cars. If they do then those of us living in Canada without a garage to store our electric cars are screwed as far as charging goes within the optimum temperature range. Now we will not only have to plug in to charge but also run a battery heater/cooler to be in the optimum range. With a local temperature range of from -30c to over +95 I see a large portion of any savings in operating cost disappearing.

I came here hoping to learn something new since I've done my own research. It makes sense to use the cells optimally. Paul314 asks good questions. Li-ion batteries are almost always designed with a BMS (battery management system) circuit that is either part of the batt pack or incorporated into the phone/car/tool/gadget, and its job is to keep things humming at proper levels. I am surprised though to see that automotive batteries should not be charged below 50deg F/10deg C since so many electric cars in my neck of the woods are being used in the winter at well below that, and not all are kept in indoor garages. Of course, if you plug it in at the end of your day the batteries will be within that temp range. Extremes and fast charging means a shorter life span. Milwaukee has a charger, fast charger, and recently, a supercharger, for those who can't be bothered to wait.

Tesla owner here. One can argue the precise specifics, but IMHO the author got all this right and frankly his advice is fairly well accepted at this point. KInd of like saying brushing your teeth is a good idea (it is). As Elon Musk pointed out, you might be able to do a tiny bit better by charging to less then 80%, but it is "not worth it." Setting the default maximum State of Charge in a Tesla to 80% for everyday driving is super easy with an icon that your finger slides left and right. Similar settings for cell phones and other devices would help a lot.

sidmehta, the infamous memory effect generally does not apply to lithium ion batteries but does apply to at least some NiMH batteries, which have a totally different chemistry.

Why don't or can't current smart phone batteries be set to charge only up to 80% at night instead of always going up to 100%? Why don't cell phone manufacturers allow the option for fast or slow charge rates? Let me guess -- to do so would extend the batteries life cycle and decrease the need for you to buy an expensive replacement. Prove me wrong!

To the folks concerned about charging a phone to “100%” not being good for battery durability... how do you know a well designed smart phone Battery Management System is not already protecting you from that? ;-)....

The “100%” displayed on your phone is simply an analog to the battery voltage. It would be very easy for phone manufacturers to set 80 or 90% of actual fully charged voltage to display “100%”....

Given Apple’s recent method to charge to 80% earlier in the night, slowly, and then to top of the battery in the last 15-30 minutes before your wake cycle, it would not be surprising that they also set 80-90% actual charge to display “100%”. (Apple claims that last 20% is hardest in the battery and therefore delays it. GO BLUE!

This is good advice if you are charging individual AA or AAA cells. This probably doesn't apply to things like cell phones. iPhones specifically have built in intelligence to maintain a healthy battery. They don't overcharge. My iPhone 11 now shows a message at night when I put it on the charger that it will charge slowly overnight with a target of full charge at the time I usually wake up. This also applies to iPads and iMacs. Probably similar story for new versions of Android devices.

I guess Robomow is out of luck!

I see opportunity to build in smart charging to the optimal conditions automatically. When recharge is done, the charger shuts down by itself. We should not have to be mindful and go unplug it. It should charge to 80%, unless the user toggles something to request a full charge. These no doubt are very easy to do today, and vendors can sell them as green features as well. Obvious, correct? No reason we should have to study "rules" and be ever mindful to obey them. Put the rules into the charge algorithm, so we can focus on bigger things.