With all the hoopla around the new iPad getting a little bit toastier than its predecessor, Dr. Raymond Soneira is in high demand these days. Yesterday, he explained how the demanding Retina display and brightness levels affect the iPad’s run time. Today, he’s back at it, warning the device keeps charging even when it claims to have been filled.

Is this an iOS software flaw akin to a “bug” in cellular signal levels on the iPhone 4 (later fixed with a software update)? Hard to tell. All we know is it keeps charging for as much as an hour after the battery gauge hits the 100 percent mark. This, too, might explain why some people experience shorter run times with the new iPad versus its predecessor…

In a short email interview with Cult of Mac, Soneira explains why folks should keep recharging their new iPad for longer than iOS claims:

I measured the power actually drawn by the AC adapter and found that the new iPad continues to charge for up to 1 hour after it claims to reach 100 percent.This affects the battery run time if you stop charging when it says 100% percent.

It’s unclear whether this issue affects other iOS devices running iOS 5.1. The article says other devices do this as well, but stops short of specifying whether Soniera was referring to other Apple devices or those from other vendors.

Soniera also confirmed his findings to Charles Starrett of iLounge, saying the device continued to draw 10W of power from the included Apple 10W Power Adapter for up to one hour after reaching what is reported by iOS as a full 100 percent charge.

In iLounge’s own testing, the new iPad “switches from a lightning bolt (‘still charging’) to plug (‘done charging’) battery icon five to ten minutes after reaching 100 percent”.

Also, this:

Notably, iLounge found unusual, non-linear reported battery drain during our numerous battery tests, with the third-generation iPad sometimes reporting a battery loss of just two percent over the first hour of testing, then averaging 10% of loss each hour afterwards while performing the same tasks.

Take into account that Dr. Soneira knows this stuff inside out.

According to his LinkedIn profile, Soneira is president of DisplayMate Technologies Corporation of Amherst, New Hampshire, a company specializing in scrutinizing computer and mobile displays of all flavors.

DisplayMate compared a 2,048-by-1,536 pixel resolution Retina display to those found on other popular smartphones and tablets. They were pretty impressed overall and noted dramatic improvements in sharpness and color saturation on the Retina display, saying “they are now state-of-the-art”.

So there you have it: don’t use full brightness with your new iPad (who does, anyway) and leave the device charging a little longer than iOS says and you’ll be fine.

We’re eager to hear from our readers who own the new iPad about this phenomenon. Did you experience longer run times when leaving the device charging past the 100% prompt?

Meet us in comments.