I have what appears to be a very old Dallas DS1216.
Installed into it (piggyback) was a 8k x 8 SRAM.
There is a video on youtube (*1) which talks about hacking in an external 3V cell however mine is an older design.
Mine has no B, C, D, E variant marking on the pcb and the internal chip is DIP14, not DIP16. There are two batteries potted into the underside but the wiring isn't the same as the DIP16 version.
Based on the datecode it looks like a 1986 part.
The Dallas 1988 databooks I found online reference a DS1216, DS1216C, DS1216E, DS1216F. The last (2011) Maxim datasheet which is what is commonly online references "SmartWatch RAM (DS1216B/C/D/H); SmartWatch ROM (DS1216E/F)"
My question (finally :-) Is the DS1216 without a suffix what is now referred to as the DS1216B?
1:
]video on Youtube