I’ve got a simple question - but I can’t seem to find a simple answer.
There must be well over a billion devices out there that use lithium-ion batteries. Smart phones and even old plain candy bar cell phones, iPods, iPads, Blue-tooth accessories, and dozens of other things that can be recharged.
But try to find the best way to charge the device so that the battery will last the longest and you’ll find dozens of different, often contradictory,‘expert’ responses.
Some manuals say to charge it every day. Others say wait until it’s down to 20 or 30 percent. Some say never let a lithium battery go down to near zero, others say to do that every few months.
In an Apple store I was told three totally different ‘bests’ by three different geniuses, all in the same hour.
Is there a scientifically proven set of instructions for maximum battery life for lithium batteries?
With modern charge controllers, it really just doesn’t matter that much. Roughly speaking, the lifetime will go down with the total energy you pull out of it. So, it doesn’t matter too much if you discharge it to 50% 200 times or to 0% 100 times.
Unprotected cells do experience severe damage if they are discharged too much–below around 15% comes to mind. But today’s devices won’t let you do that, and will “lie” to you about the capacity–what you see as 0% is really more than that. The same goes for overcharging; the device will shut down the charge before it’s a problem.
All that is not to say that there are no differences at all between strategies, but to a first approximation there’s little difference.
According to the (newly updated) Llifehacker article earlier today… Perform shallow discharges. Instead of discharging to 0% all the time, lithium-ion batteries do best when you discharge them for a little bit, then charge them for a little bit. The table below, from Battery University, shows that discharges to 50% are better for your battery’s long-term life than, say, small discharges to 90% or large discharges to 0% (since the 50% discharges provide the best number of cycles-to-usage ratio). Don’t leave it fully charged. Similarly, lithium-ion batteries don’t need to be charged all the way to 100%. In fact, they’d prefer not to be—so the 40%-80% rule you heard is a good guideline. When possible, keep it in that range to prolong its life as long as you can. And, if you do charge it to 100%, don’t leave it plugged in. This is something most of us do, but it’s another thing that will degrade your battery’s health. If you need to charge it overnight, use something like the Belkin Conserve Socket to stop it from charging after it’s full. Fully discharge it once a month. This may seem contradictory, but hear us out. While lithium-ion batteries shouldn’t be discharged regularly, most modern batteries are what’s known as “smart batteries”, which means that they can tell you how long you have until your battery dies (e.g. “2 hours, 15 minutes remaining”). This feature can get miscalibrated after a lot of shallow discharges. So, manufacturers recommend fully discharging your battery once a month to make sure this stays accurate.
You can see from the discharge table that number of cycles times discharge amount is close to equal: you get the equivalent of roughly 500 full cycles. The 50% point does a little better than this but not hugely so.
I don’t buy the “don’t leave it fully charged” line. Again, modern charge controllers are designed to handle this stuff for you. It made more sense on older devices with less smarts. Taking the battery off the charger means you’re now draining the battery again, which will eat into your total cycles.
This is a real thing, but you should note that if you intentionally discharge the battery, you are wasting cycles. It’s a fine idea if you’re using your device normally, but probably a bad idea if you’re artificially running down the battery.
You know, we go though this over and over again. There must be a dozen threads on this topic. Dr. Strangelove has it right. But, I’d like to add the trying to micromanage your battery charging is a fool’s game. First of all, most modern devices will be obsolete before the battery is useless (my original iPhone from 2007 still has a working battery, even though it’s been replaced by two newer phones). Secondly, trying to eek out a time bit of extra life by storing a device 50% charged means that if you ever need to grab it and go, you will only have 50% of your possible runtime - which sort of defeats the purpose of having a long-life battery.
ETA:
FWIW, I leave all my devices pulled in and charging whenever I’m near a charger. My 2011 MacBook still gets almost 9 hours on a charge…