Battery compartment was pretty simple, I made it to hold the two different types of batteries I use which are Hyperion 4S 2500 mah(short and fat pack) and the GensAce 4S 2500 mah which are long and skinny.

This is my battery compartment, I used the two stock spars to hold the GensAce batteries as they fit almost perfectly between the two. I constructed a floor for the compartment using small pieces of 1/8" ply and 1/4" bass wood as can be seen in this photo. You can see where I carved out the two spars so the fatter Hyperion battery could slip between the two spars and rest on the floor. There are spacers in there to keep it from moving around, this set up works quite well for what I needed.

This photo shows a GensAce 4S 2500 pack sitting as she should ready to be locked down. If you notice the two small pieces of wood, one on the top of each spar, they are just popsicle sticks that swing over and across the top of the batter to lock it down. They work very well and are easily replaceable.

Battery locked down in place.

Figured I would show her off since I painted the lower cowl and wheel pants last week. Paint is a little darker than I wanted but that's ok, still love it!
Hope this helps you.
John
PS-I was able to fly her again this weekend, listen how quiet these babies are!!