Yesterday, in our review of the iPad, we mentioned the issues we were having charging through our Dell's USB port. Plug it in and we get a “not charging” notification message, even though the manual says that it should "charge slowly".
Turns out, the problem isn't us. The iPad requires a "high-powered" USB port to charge normally—a port that is only found on the latest Mac notebooks and desktops. So if you have an older Mac or a Windows-based PC, the iPad will, at best, only charge slowly and only while it is not turned on.
It also doesn't help that the included power cord with the iPad is so short that it is difficult to charge while in use, even using a wall outlet.
While there are still a lot of things I like about the iPad, the charging bit gets a big thumbs-down.
From Khürt Williams on April 07, 2010 :: 11:29 pm
I think the iPad is the first USB powered device that requires a high powered USB port. I have seen a few external hard drives that won’t run at all on the lower powered ports on older computers.
The issue is that some manufacturers produce cheap non-standard compliant products: http://en.wikipedia.org/wiki/USB_hub#Power