This is genius and actually this is the next step of my new fishfinder project - great timing. I don't intend to cut any new hatches but I can use my rear hatch for this purpose. I was originally planning on just placing the battery inside the hobie hatch tray, but this improves on that design as it mostly eliminates the potential that the battery could be sitting in a pool of water.  Thank you for posting!

Cheers!

Is this front hatch on a Compass?  Looks different than any of the flipping lid type front hatches of the outback and revo, more like the middle or rear hatch of those models.  Anyway, very creative adaptation of using the hatch cutout piece as a insert for a battery pack.  It's nice to avoid batteries sitting in a pool of water.

That was the middle hatch that I  moved to the front on the 2021 compass.