Indeed, Soneira said, "Damaging the longevity of the battery is then exactly what the new iPad's internal battery charging hardware and software are doing since it is their responsibility to properly control and manage the battery recharging process. It's pretty obvious that if the new iPad knows that it is fully charged then it should automatically stop the charging! So 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."
Sure, Soneira continued, "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. Perhaps Apple should instead graciously accept my interpretation and rescind their own remarks, which sound like very poorly thought out damage control. Otherwise they need to immediately fix the iPad battery charging algorithm or they may be held responsible for replacing all iPad batteries. Which one will it be?"
If you do as Apple says you should do and "stop charging the iPad when the battery indicator says 100% you won't get the maximum running time - something that is very important to many people. I repeated the Battery Running Time measurements exactly as above, but stopped the battery charging when the battery indicator reached 100%. For the new iPad at the Middle Brightness Slider setting the Running Time decreased by 1.2 hours to 10.4 hours (10 percent). While at first sight this appears consistent with Apple's own "up to 10 hours running time" my tests were in Airplane Mode with no Wi-Fi and no activity or running Apps of any sort - just a static display. The 11.6 hour running time above for a fully charged battery would most likely deliver a real use running time of over 10 hours as indicated by Apple, but the 10.4 hour time would most likely not."
So, what's wrong here? Soneira explained, "The battery 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. Note that batteries are based on complex chemistry so there is no practical way to measure the charge level "in hardware." So there is something wrong with the battery charge mathematical model on the iPad. It should not say 100% until it actually 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."