I get the x over the battery all the time when charging from anything but the OEM Samsung AC charger. Kind of annoying. Think it just means it's charging really slow. Why did they up the charging requirements? I have a few OEM 2.1a chargers, and everyone gives the red x in the battery icon. Then I see the Samsung one is 2.5a. That tablet should not need that high amperage to charge efficiently.
That's depends on the USB power output of each computer.. It is mesured in MA.. Tablet batteries are larger than mobile batteries;thats why it needs more power than mobile phone needs.
don't computer usb ports have a set limited output to begin with? Shouldn't vary from computer to computer. Regardless, it should charge albeit very slow. If you're doing it on an overnight, turn wifi off or power it down.