The finding comes from a follow-up test by DisplayMate President Dr. Raymond Soneira, who conducted an in-depth analysis of the new iPad's Retina Display earlier this week, and claims in an e-mail to AppleInsider that a mathematical charge rate model may be the cause of false on-screen battery indicator readings.
Soneira's findings have not been corroborated and thus may not reflect all third-generation iPads, though it seems that the problem is not hardware related and instead has to do with the device's programmed charge rate.
In his investigation, Soneira found that the iPad continued to draw 10 watts of electricity for two hours after indicating 100% charge, then began to reduce power for an additional ten minutes until a precipitous decline in power draw signaled the termination of the charging cycle.
Soneira offers this explanation:
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.
He goes on to say that there may be a fault in the battery charge mathematical model in the new iPad as the indicator should not read 100% until it's power draw switches from 10 watts to a trickle charge of about 1 watt.
Apple claims the Wi-Fi version (left) can browse the web for 10 hours, while the 4G model (right) can get 9 hours on a cell network. | Source: Apple
It is unclear whether the iPad's battery level indicator shows an inaccurate level throughout the entire charging process or if the issue is limited to the final stages directly before the power management chip initiates a trickle charge.
While Apple boasts that in spite of its power hungry components like the high-resolution Retina Display and A5X processor, the third-generation iPad's battery life is similar to that of the iPad 2. These claims are no doubt based on a fully charged unit, and the newly-discovered indicator issue could confuse some customers into thinking their device is not performing up to advertised standards.