A lot will depend on which extra it is - and even if we knew, it would be hard to say.

But basically, by over powering it, you now have to compensate by adding still more weight. You could add a pound or two and the plane will still FLY well, but what you will find is that as the weight goes up, so does the wing loading - As the wing loading goes up, so does the stall speed. So you may find that your plane will not slow down on landing, or, worse yet, will tip stall on "turn to Final" if you don't keep the speed up.

I would suggest adding an extension to the battery wire and cutting an access in the covering so you can mount the battery in the tail