RTC appears to be working and keeping the date and time across cold-starts.
I picked the Epson RTC-72423 which is about a $6 chip, but is obviously directly compatible with the OKI Semiconductor MSM6242B. The design, including the battery supervisor, had never been tested — not even as a prototype… and appears to have worked the first time!
I needed to do a “setclock reset”, set the date via “Date 28-Dec-13 02:26:00” command, and then did a “setclock save” Subsequent setclock loads brings it back!
More thorough testing needs to be done, but initial indications look real nice!