I have no preference on the battery slots. I'd just like to see one actually on the buggy! Looks really nice OldTimer. You do some excellent work with the carbon fiber. I know a friend here in the states that could use one for sure. At our last race, he broke the battery strap rods completely off the chassis with the strap still attached with the body clips, and he cracked the front of the chassis really bad as well. First time I've seen the stock carbon composite chassis break.
Just curious, are you selling your stuff to any distributor in the U.S.? The shop I purchased my ZX-5 from has some carbon fiber parts that look remarkably close to yours:
www.evolutionhobbies.com.
If you are selling to U.S. distributors, I'd love to see one of those chassis over here.