I have a 1964 Accutron D87757 case number with the the above battery. I need to replace it and have contacted 3 sources, to date, without positive results. Best hope so far is the Energizer 392/384 that appears in the photo to be closest. I'm still awaiting word from that source. The RW51 has the positive side on the smaller diameter portion of the battey. Last attempt was a Duracell 301/386 that is the same size diameter but the polarity is reversed and it would not fit.
If someone can help ID the correct replacement battery, it sure would be appreciated!
The RW51 is replaceable with the Energizer 387s, which has a spacer ring with it. As far as I know, there is no direct Renata equivalent, although if you have the spacer, you might be able to re-use it with another battery. It says '394/380+spacer on the package, so I'm guessing a 394 would work with the spacer added.