That's talking about a backup battery for the real-time clock on the phone. That type of battery is usually not rechargeable and doesn't support enough power to

That's talking about a backup battery for the real-time clock on the phone. That type of battery is usually not rechargeable and doesn't support enough power to make any sort of call. I've never heard of an emergency backup battery for just the 'baseband' in any phone, but I am open to being proven wrong.