I have an Advent.
Having visited the site that Sold Advent approved batteries, I then looked around the net and found a suitable battery, It works well.
However, The original battery had the compartment cover built into it and that end of the cheap one is different, so it looks a bit odd.
As my Laptop is for work only, and not a Status Symbol, it is of little consequence.
However, your son may see his Laptop in a different light and be less than happy with such a difference.