The battery indicator on the iPad is a liar. Research from a display research company says Apple's new tablet continues to charge for a long time after the onscreen indicator shows it's full.

Ray Soneira of DisplayMate— whose research also showed that the new iPad's retina display drains significantly more power than previous models — conducted a test that showed the iPad kept drawing power at the full recharging rate of about 10 watts for two hours after it initially reported having a 100% charge. Only at 2:10 did the recharging "fully terminate" with a sudden drop in power.

Soneira says he wasn't setting out to test the battery, and that he only looked at the iPad's power usage to see how much is going to the screen. However, when he noticed his equipment told him his iPad was charging even though the screen said "100%," he decided to study the issue further. That's when he discovered the extended charge time.

Why would the iPad say it has a full charge when it doesn't? Apple isn't saying (a spokesperson didn't respond to a request for comment), but Soneira has a theory.

"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," he told Mashable in an email. "It's actually rather difficult to do because most batteries degrade slowly and then tend to surprise with a precipitous decline near the end. So there is something wrong with the battery charge mathematical model on the iPad."

The takeaway for users: If you want a full charge (for, say, your next flight), don't trust the display and be sure to keep your iPad charging for at least two hours after your iPad says it's had enough. Or better yet, simply leave it plugged in overnight when it's time for more juice.

This isn't the first time Apple has had problems with display indicators on iOS devices. Back in 2010, amidst the iPhone 4 "antennagate" flare-up, the company re-examined the signal-bar icons on the iPhone, and found them to be inaccurate. Soon after, Apple released a software update that addressed the problem.

How important is battery life to your tablet, and do you think this is a serious problem? Sound off in the comments.

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