So a little google searching meant I was finally able to find the answers i needed.
It seems it's a Dell 10 battery, and the grooves aren't quite as deep as the 10v. (Yeah thanks a lot Dell).
Anyone having the same problem, take a small phillips screw driver (i found a craft knife just wouldn't do the job). and bore a hole inside the hole where the bracket goes, until you reach the connector underneath, but be very careful towards the last few mm of plastic, so you don't force it too hard and break something.
Once you're through, gently take a thin file and rotate it in the hole to clean/remove and jagged edges.
Then flip your mini over, slot the battery in and push the clips back into place. Don't force them, if they won't go, file a bit more off each time.
Hopefully this will help anyone who encounters a similar problem.