Quote:
Originally Posted by BananaPancakes
I do it occasionaly. For example, sometimes my laptop says my battery is fully charged when it's only at 94-96% (says my iStat widget for my Macbook -I don't know if there's a windows equivalent). After I fully discharge my battery and charge it up again, it charges all the way up to 99%. I've had my laptop for almost 3 years and I've done this maybe 3 times.
I don't know if this is healthy for the battery, but at least I'm getting a full charge after I do it.
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There's a couple things going on here. First, you should never discharge al the way down below 20% if you can avoid it, because it definitely hurts LiIon cells, and will reduce their service life.
The only time you want to discharge LiIon batteries all the way down is if you suspect the calibration information is incorrect. In other words, if your laptop is reporting too much or too little run time left. In these cases, the power management software doesn't know exactly how much charge is currently in the battery, and so it can't report on how much run time you have left accurately. By draining it all the way down, and fully charging in one sitting, it re-learns how much juice you can extract, and how much a charge cycle puts back. On my ThinkPad, it will actually request a calibration cycle if it detects its out of whack, I don't know about other laptops though. I know there are Apple support docs on fully draining the battery and fully charging it to automatically calibrate the battery, but I wouldn't use it unless you are like 30% out on those estimated times. Doing it once a year on any kind of laptop isn't going to hurt that much though.
In 8 months of use on my Thinkpad, it has never asked for a calibration, by the way, after I performed an initial one when I bought it.
Second, when you charge a laptop fully, and it stops somewhere between 90-100%, that is often a feature again of the power management software. Putting the last 10% of capacity into a battery is also stressful for it, just like using the last 10%, so if the software detects that you frequently use your laptop plugged in, and don't frequently drain down to low levels, it will stop at less than 100% because you don't need to use that capacity, so there's no need to stress the battery further. Again, my ThinkPad handles this automatically, and you can override this behavior if you really need that additional 10-15 minutes of runtime, but it clearly states that doing so will decrease the lifespan of the battery.
In summary, any memory effect that LiIons have is less of a problem in their performance than the wear caused by deep discharge. And no matter how well you take care of your laptop battery, you have to consider it a disposable item, it will wear out, so just charge it up after you've used it on battery, don't drain it below 20% unless you really have to (like in a presentation, say), and enjoy.
Hope this helps, I've researched it a lot, both for my laptop, and for other uses like model aircraft, where the Lithium batteries cost big, big bucks, and are subjected to hard use running the planes.
Battery memory problems?
