Soneira found the problem during his iPad 3 benchmarking. He measured "the power actually drawn by the AC Adapter and first found that the new iPad continues to charge for up to 1 hour after it claims to reach 100%. This affects the battery run time if you stop charging when it says 100%." This isn't just an iPad 3 problem. Soneira notes that "Other tablets and smartphones also lie about their charging status."
Further testing by Soneira has shown that "At 2:00 hours after reporting 100% charge the new iPad hardware started to reduce the charging power. At 2:10 the recharging cycle fully terminated with a sharp decrease in power." Thus, "The new iPad battery is truly fully recharged 2 hours and 10 minutes after prematurely reporting on screen that it was fully charged."
What's caused this? Soneira speculates, "The charge indicator on all mobile devices is based on a mathematical model of the charge rates, discharge rates, and recent discharge history of the battery. It uses this information to estimate how much running time is left. It's actually rather difficult to do because most batteries degrade slowly as they discharge and then tend to surprise with a precipitous decline near the end." I think we've all seen that!
But why is the iPad 3 so badly off in its estimate? Soneira thinks, "There is something wrong with the battery charge mathematical model on the iPad. It should not say 100% until it stops recharging and goes from the full recharging rate of about 10 watts to a trickle charging rate of about 1 watt. Otherwise the user will not get the maximum running time that the iPad is capable of delivering."
That full battery charge, according to Soneira's benchmarks, is impressive. At the middle brightness setting the iPad 3 can run as long as 11.5-hours. Since the new iPad has "4 times as many pixels in the display that need to be kept powered [over the iPad 2 and} 4 times as much memory and processing power is needed for the images. In addition, the light transmission of the LCD decreases as the pixel density increases, so a brighter Backlight is necessary. In fact, the number of Backlight LEDs has roughly doubled (from 36 to an estimated 72 to 82), so the Backlight power has approximately doubled. Since the display normally consumes about 50-60 percent of the total Tablet power, the new iPad needs at least a 50 percent larger battery. In fact, the battery increased from 25 to 42.5 watt hours, a 70 percent increase."
The iPad 3's battery life is remarkably good.
Somehow, Apple has managed to significantly increase the iPad 2's power density of its Lithium-Ion batteries. In that the key may lie as to why its battery charger is giving incorrect information. Its battery charge mathematical model, and/or the algorithms used to come up with the recharge numbers may simply not have caught up with the iPad's new battery technology.
Or, Apple may have just been "fibbing" about the recharge time. When it comes to battery-issues, most companies share the truth about how long a battery will actually be useful and how long it takes to recharge them. And, last but never least, how people use their battery-powered devices vary wildly and largely determines what really happens with their useful life.