As we told you last week, unplugging your brand spanking new iPad as soon as the battery gauge hits the 100 percent mark entails missing out as much as ten percent of additional run time, or about 1.2 hours. This has been attributed to the iOS battery algorithm, which kinda brings back old memories of a bug in reporting cellular signal levels on the iPhone 4, later fixed with a software update.

According to new findings, this is actually a system-wide behavior in Apple’s mobile operating system – thus affecting older iPads, as well as your iPhone and iPod touch. In fact, all iOS devices are affected by what’s been called “busted” battery algorithm, it’s just more pronounced on the new iPad due to its 70 percent more capacious battery.

What exactly is going on here, you ask…

According to Adrian Kingsley-Hughes over at the ZDNet blog, this behavior has persisted in iOS and is actually affecting all iOS devices rather than just the new iPad. He thinks it’s by design: Apple is displaying the 100 percent charge indicator at a lower capacity of around 97 percent in order to keep the battery “safe and healthy”.

The author explains:

The battery on the new iPad is huge, with a total charge capacity of a massive 42Wh or measured another way a monstrous 11,666 mAh. A 3 percent safety margin for the iPad 2 battery would be equal to around 210 mAh, while the same safety margin for the new iPad would be equal to 350 mAh.

The crux?

The wrinkle is that when the iPad 3 battery indicator first says “100%,” the battery is actually only 90% charged and you get 1.2 hours less running time. However if you recharge your iPad 3 unattended (and off or in sleep mode), especially overnight, you will get the necessary extra charging time to achieve its maximum running time.

According to DisplayMate, the device takes over 5.5 hours to fully charge when off or in sleep mode and up to a whopping 20 hours with the display set to maximum brightness. Recall, if you will, that DisplayMate also blamed the iPad’s Retina display with twice the LEDs for shorter run times and the widely reported overheating issues.

Now, here comes the really interesting bit.

Perhaps not surprisingly, Soneira might have damaged his own reputation by stating Apple’s supposed claims of how overcharging your new iPad allegedly could hurt the battery inside. Strangely, Dr. Soneira did not provide a link to Apple’s website proving this.

According to Apple, the new iPad is configured to damage the longevity of its own battery if it isn’t manually disconnected from the AC charger when the 100% indicator appears. Anyone that recharges their iPad unattended, especially overnight, will be doing this. While Apple’s remark might apply to recharging dumb battery operated toys, the new iPad is a very sophisticated and expensive computer device that is fully capable of properly controlling and managing its own (rudimentary) battery charging process.

Information provided on Apple’s website makes no mention of any of this and Dr. Soneira backtracked later. Meanwhile, CNBC relayed Soneira’s logic and said overcharging will actually harm the longevity of the battery.

I know what you’re thinking, big media, right?

Indeed, one would think CNBC should exhibit some expertise about how lithium battery technology works. The charging circuitry in lithium batteries prevents damage by automatically halting the charging process once the battery reaches its full charging capacity, putting it on a trickle charge that keeps the battery at or near 100 percent.

Batteries Apple puts in its iOS devices typically supports up to a thousand full charging cycles. Afterwards, the battery capacity slowly begins to diminish over time. The company educates customers how “a properly maintained iPad battery is designed to retain up to 80 percent of its original capacity at 1000 full charge and discharge cycles”.

I don’t know about  you, but I’d expect the iOS battery gauge not to lie about charging. I mean, a 100 percent should always be a 100 percent, right?