I'm shaking my head. Since I bought my airplane in September 2019, my mechanic and I have been trying to locate the battery pack. We have gone through a couple of annuals following wires that disappeared without results, while I gathered the comments and service kit that improved the box and battery type.
With the panel upgrade on this third annual, now was the time. Lou finally found it, tucked up as far back as possible and hidden. Handling it, it feels like a sticky bomb from the tape being heated due to the location.
Here is the text where he sent me a picture, and you can see my comments.
The four D Cells are soldered together, duct-taped together, and wired into the system with automotive connections.
More to say about this, but need to get going...