Made a purchase last night for this - I've been running the Eggtimers on 9V batteries, exactly as Cris tells you not to like 50 times in the manual. It's worked, but exactly as he described the Wifi is kinda flaky at that point. So, switching over to 2S Lipo as recommended.
I purchased 1S batteries and will run 2 in series. BetaFPV has a really neat battery that is in a long/skinny form factor that works really well for this rocket's av bay.
https://betafpv.com/collections/batt-1s/products/bt2-0-450mah-1s-30c-battery-4pcs
They have 260, 300, and 450 mAh options. I'm going to go with 450s for the computers (one set of batteries for each computer) and 300's for the deployment channels (for those who haven't worked with Eggtimers, you have the option of powering the computer with one battery and firing the charges with another battery, so as not to brown out the computer when firing the charge).
Absolutely awesome little thing, they actually sell 2S pigtails, already wired up for running 2 of these batteries in series.
https://betafpv.com/products/2s-whoop-cable-pigtail-bt-2-0
Printed the first take on the "pod", got some changes to make for sure...the "tunnel" that the camera resides in is too deep, so the whole point of putting it near the bottom for a better view is moot with the current design. Also, after feeling it, I'm sure I can make it shorter (protrude less into the airstream) without messing up the structural integrity, so going to do that. Also think there's room to "sink" the battery and camera into the side of the fincan and make the pod shorter...which seems like a great use of 3D printing (to make something that while otherwise possible is a lot more difficult) but I'd be worried about the strength. Maybe. The way the fincan is designed, the bottom 8" or so carries all the load (the tube doesn't go all the way to the bottom), so I'd be asking a lot of the 3d printed material. Things to think about on a cold Saturday in Wisconsin.
...Making progress on both the L3 and this one at the same time. Crazy.