Although it's a nice feature to have, and I have dug out a Hitachi 6116LP specially for the occasion, it's not a priority for me. So, in your own time.
In the days when the only way to get code into the machine was to first type it in and thereafter load it from a tape, it would have been a brilliant asset (which is no doubt why Buzby took the trouble to battery-back some of his memory on 'Micky').
We use through-hole CR2032 type coin cell holders in a couple of products at work, but I don't know yet whether one of those will just drop in.