Fluke discontinued and recalled the 1AC line of voltage testers. That happened so long ago, that they aren't honoring the recall anymore. The unit I have is 20+ years old, and the battery cap broke.

I designed this cap in Fusion 360 to easily screw on to the end of the device, fit snugly enough to provide a strong mechanical connection, and work with the battery spring.

I printed this in PLA, but if you are going to leave it in a tool box that gets warm, it may be better to print it in PETG for long-term use.