I designed a battery tray to fit my "Josh Bixler's" Flite Test Gremlin Frame, this allow for quick battery changes and provided some battery protection around the sides. It also secures the battery to the drone better not allowing for a battery to disconnect on a "hard landing" allowing the user to still have power to the beeper(hopefully you have one of those on your gremlin) to find the quad easier.
The battery tray mounts to the bottom of the bottom gremlin plate and allows you to use the existing screw locations on the frame to secure it, all you need to do is add a strip of Velcro under the tray and around (or use the original elastics bands method of attaching the battery if you prefer).

The battery I am using in this tray and know it will fit is a 35c 850mAh 2s Lipo battery or similar.
Shown in the picture is the V1 design

I have listed 3 version 2 were made for PLA and the 3rd design is for TPU
V1 and V2 are similar except I have added some extra supports on the sidewalls V3 was designed to be easily printed with TPU.

Anet A6

No

Yes

.20

40

These settings are for PLA only.