Some true asshole manufacturers store critical data in a prom. They solder the batteries in and if you remove them and it loses power the prom clears bricking the device. C/KU band satellite receivers do this. As well as many older cable tv boxes. I used to repair them and had bench power supplies to keep the prom alive during repair. At the end of my run with the cable industry I had started cloning the proms and replacing the information that they stored there.