These are the parts that I printed to restore an old flashlight. The battery buffer fills a void in the handle that made the batteries loose. The new convex lens helps to focus the light a bit more than a flat pane of glass would. It's not tremendously effective but it makes the light work well enough for everyday use.

The battery buffer is sized for a D battery.

Watch the restoration here https://youtu.be/0USeHuIvZgs

Formlabs

Formlabs Form 2

Doesn't Matter

Yes

50 micron

Doesn't Matter

The battery buffer can be FDM printed but the lens is definitely a clear resin print only. I used a Form 3 but I imagine any resin printer would work for this. Lens polishing required in all cases. Support the lens on the outer rim only!