This is a divergence meter as seen in Stein’s Gate. It uses Tom Titor’s excellent design. It can run from a power adapter or from a 9V battery inside the case:
The original design uses a standard 9V battery as the cordless power source. This typically lasted anywhere between 10 minutes and 45 minutes, and when it ran out you had to open up the case to replace it. A bit of googling around showed that you could get rechargeable LiPo ‘9V’ batteries and that these would last around three hours. Much better. However, I also found a little charger module for these batteries, so I shoe-horned that in and re-wired things a little so it would act as a load-sharing charger (which means it will charge the battery and power the clock when the clock is plugged in). Here is a little timelapse video of it running off the LiPo 9V battery:
I wrote this mod up on my blog.