I hate to disagree......but I'm going to anyway!
I've not seen this fabled 10% mentioned at all by Apple however, in terms of calibration Apple do recommend that you run a full cycle once a month, that is running it all the way dwn and a full charge.
As for battery life and how to maximise it, Apple themselves provide some great advice here.....
http://www.apple.com/uk/batteries/
http://www.apple.com/uk/batteries/ipad.html
The Archangel
Yes, I would tend to think now that the "fable" about Apple's recommendation may have developed gradually in my mind. I also agree that in your two links Apple is saying that you should run a full cycle once a month and, as you have quoted, "Running it all the way down", presumably to zero flat charge.
But Apple's advice IMO has not kept up with latest research, which is now generally indicating that it is not good for the overall life of the battery, to run it down to zero. In fact I believe Apple's advice goes right back to the iPad2 and has not changed since then.
There are now a number of authorities, this is one I could quickly find, who clearly say:
1) It's good to recharge the iPad often without having taken it down to completely empty.
2) It's not good to completely discharge the battery to absolute flat.
Here's one quote I could quickly find (TechRepublic) which seems indicative of the latest expert thinking.
1: Keep your batteries at room temperature
That means between 20 and 25 degrees C. The worst thing that can happen to a lithium-ion battery is to have a full charge and be subjected to elevated temperatures. So don’t leave or charge your mobile device’s battery in your car if it’s hot out. Heat is by far the largest factor when it comes to reducing lithium-ion battery life.
2: Think about getting a high-capacity lithium-ion battery, rather than carrying a spare
Batteries deteriorate over time, whether they’re being used or not. So a spare battery won’t last much longer than the one in use. It’s important to remember the aging characteristic when purchasing batteries. Make sure to ask for ones with the most recent manufacturing date.
3: Allow partial discharges and avoid full ones (usually)
Unlike NiCad batteries, lithium-ion batteries do not have a charge memory. That means deep-discharge cycles are not required. In fact, it’s better for the battery to use partial-discharge cycles.
There is one exception. Battery experts suggest that after 30 charges, you should allow lithium-ion batteries TO ALMOST (my emphasis) completely discharge. Continuous partial discharges create a condition called digital memory, decreasing the accuracy of the device’s power gauge. So let the battery discharge to the cut-off point and then recharge. The power gauge will be recalibrated.
4: Avoid completely discharging lithium-ion batteries
If a lithium-ion battery is discharged below 2.5 volts per cell, a safety circuit built into the battery opens and the battery appears to be dead. The original charger will be of no use. Only battery analyzers with the boost function have a chance of recharging the battery.
Also, for safety reasons, do not recharge deeply discharged lithium-ion batteries if they have been stored in that condition for several months.
5: For extended storage, discharge a lithium-ion battery to about 40 percent and store it in a cool place
I’ve always had an extra battery for my notebook, but it would never last as long as the original battery. I know now that it’s because I was storing the battery fully charged. That means oxidation of lithium-ion is at its highest rate. Storing lithium-ion batteries at 40 percent discharge and in the refrigerator (not freezer) is recommended
It is this TO ALMOST discharge, say after 30 charges (about monthly for most busy users), coupled with my other reading about Lithium Ion batteries, that has helped to build up that "minimum 10%" in my mind. Seems a reasonable figure to me though, as it does not mean completely dead flat discharge as implied by Apple.
But yes, I seem to have incorrectly quoted Apple.
Regards, Andrew
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