I once worked on a product that you really did not want to have not coming back up. I was on it several years after the original engineers had designed an early model. Said engineers had not tested what happened when the CMOS battery died and triggered a reset of BIOS settings, brought it back to the hardware platform’s default state. When it did, the thing entered a non-bootable state. You could, with a serial port, access the BIOS and fiddle the settings back for one good boot…but the CMOS battery was non-removable, soldered to the motherboard. Our manufacturing process had not involved changing the default BIOS settings, just what was stored in CMOS. Oops.
IIRC our customer care guys just sent out new models for free to affected customers – the original hardware model wasn’t sold in large volume, and the cost of the actual hardware components wasn’t especially large relative to the cost of the product.
I had one sitting around on my desk, as it was sometimes handy to have a physically-accessible device to do work on. I rolled down to Radio Shack – yes, this was a few years back – got a removable CMOS battery case, stripped the non-removable battery out, soldered the battery case to the motherboard, and had the only instance of the device out there that could take a fresh CMOS battery.