With the new iPad, there are conflicting reports as to exactly how long the battery needs to charge before being at full capacity. Many say that the new iPad’s battery isn’t at 100% until one hour or more after the battery icon indicates it is. Apple says that isn’t true.
What actually happens is the iPad, iPhone, or iPod touch reports a full charge slightly before it’s at full capacity. The device then charges to full capacity, discharges a bit, and recharges back to full capacity. This cycle repeats until you unplug the device.
Tchao says Apple designed the circuitry “so you can keep your device plugged in as long as you would like.” That’s why you don’t have anything to fear when plugging in your iOS device overnight.
With this iOS feature, your device should always get its maximum amount of battery life no matter how long it charges after the battery indicator hits 100%.
Remember that the iPad, and essentially all other recent modern devices, have Lithium-ion batteries. These batteries have a limited lifespan, and don’t need to fully drain to get the most performance. If your batteries don’t last as long as they should, it’s likely because their capacities have decreased over time, which means they hold less charge.
The battery inside the new iPad is massive compared to the one inside the iPad 2, so it takes longer to charge. The iPad needs the larger battery for the Retina Display and quad-core graphics. The large battery also makes it possible for the new iPad to function as a mobile hotspot for more than a full day.