Components for Building Computers From Scratch/USB Project
If I take a USB Cable A to mini B and cut the A off.
Then just hook the Red and Black wire to a 9 Volt Battery.
I can conect the mini B end to my Tablet.
Not a standard Carbon Zinc 9 Volt Battery will give 400mHA.
And a USB port will give 500mAH.
So I know I am under the AMPs.
And the 9 Volt Battery is DC so I know this is ok.
What do you think of this Project?
I think you risk considerable damage to the tablet - the USB standard specifies 5VDC, not 9VDC. The battery's output voltage is far too high to be considered acceptable for the tablet. Even if you brought the voltage down, there is no regulation on the discharge of the battery which can be dangerous for the battery. Further, the tablet could very likely drain the battery fairly quickly, making this a relatively ineffective way to charge or extend the tablet's life.
There are commercial products that will act as external batteries/chargers for devices that charge or can draw power from USB, which are much safer, such as this device from Duracell: http://ww2.duracell.com/en-US/product/instant-usb-charger.jspx
Alternately, there are solar-powered devices if you have access to the sun (for example if you're taking the tablet on a hike), like this one: http://www.amazon.com/Levin-trade-Rain-resistant-Shockproof-Portable/dp/B00JEGLL
In general I would NOT suggest what you're proposing to do, and would highly encourage you to purchase a commercial product that is designed to operate safely and stably for your intended goal. Fortunately, neither type of product is terribly expensive, nor terribly complicated, so it should not be too much of a problem to go that route.