Herb Johnson via vcf-midatlantic writes:

There is a literal "mod" of Dallas chips:

http://www.retrotechnology.com/herbs_stuff/sgi_battery.html

wherein you slice into the epoxy package and splice in a watch battery. if this is the mod you are doing, I'd be glad to reference any Web page you have about doing it.

There are likely some old versions of the Dallas time-of-day chip and RAM which have no modern version. That said:

VAXman posted:

...

The DS1287A was fairly common TOY clock back then. You can replace it with > the newer DS12887A. Goggle it, there are ample sources.

...one has to replace it with a compatible device, and it's a bit of work and luck to determine if any replacement is likely to work. Whereas, you have the chip-in-hand, that only has a dead battery.

Well, the DS12887A has worked well for *all* of my VAX and or Alpha systems that were equipped with the DS1287A. That "slicing into the chip" hack to add a battery has seen serveral re-incarnations over the years whenever the topic of replacement arises.