Make something like a bullet puller.
Imagine if you could put a handle on the light so that it was shaped like a hammer, with the ZL being the hammer head.
Next you'd tap (or whack) the handle near the ZL/head. The ZL will accelerate faster, leaving the battery behind.
Multiple lighter taps are probably better for the light than a whack, ramp up as needed, and of course don't hit the light.
A green branch split down the middle partway and lashed to the light would be quick and easy and probably work fine. Whack or tap with another section of the same trimmed branch, or a wooden handle. It's about accelerating the low mass of the flashlight faster than the friction in the tube can hold the mass of the battery, so the whacker should be light weight.