Advent Vega for Sale comes boxed with all the bits it is running Vegacomb but the original advent rom can be puit back on or you can easily put any rom you choose. Few light scratches on the rear case but screen is mint.
£50.00 ono
Or will swap for a rasberry PI

how old is the advent ,what size is it., I have a rpi ,I might be interested in a swap .

Its 10.1" and its roughly 2 yrs old. Plus it is running the original rom not Vegacomb but it is very easy to install other roms to it.

how long does the battery last for .

Depends what your using it for checking email and general surfing will last the day no prob but playing resource hungry apps or games like angry birds/temple run you will get about 6 hours out of it.