This shim will fill the battery cavity with ~1cm of space to allow room for battery wires. Scale by the Y axis to make thinner or thicker for your battery. This also protects the battery lock and battery from side hits where a shell might not cover the battery.
I do suggest printing this in tpu with 10-20% infill to allow wiggle room. It's a tight fit.
I printed this with orange to yellow color changing tpu. This lets me see at a glance if the battery is hot but is not necessary. The pictures were taken right after pulling it off the bed so it's still pretty yellow to show the heat sensitivity.
There are two versions. The second has a lip to make it easier to grip.
The author remixed this model.