Dell Venue 8 Pro battery replacement
How is the battery replaced in the Dell Venue 8 Pro and where do I get a new battery?
An inexpensive 8-inch tablet with a premium feel. Released January 2014.
Here is a link that shows how to replace the battery in your tablet.
They also advertise that they sell batteries for the tablet. You may wish to 'Google' search for Dell Venue 8 Pro battery to see if there are other suppliers and if the price being asked for the battery by the people in the video is competitive.