Has anyone installed an additional battery pack?

[MrFish]

I have read several posts that discussed the feasibility/non-feasibility of adding a range extending battery pack but I have yet to know of an actual install and how it is working. The closest thing to a usable pack I have read about is the one that Enginer was promoting, however I have not seen a recent posts. Any thoughts and information on the subject would be appreciated.

Cheers......Mike