Terry,
I did this mod to my SRT's some time ago (using the quoted IN5711 diode which I obtained off ebay) and it works great using silver oxide cells.I find silver oxide cells best - I find they last between 3 and 5 years in my SRT.Here is a link to the SRT battery mod at Anthony Hands' Rokkor Files
site.In the first section there is a graph showing discharge profiles of the different types of cell.
http://www.rokkorfiles.com/Dickspages.htm
Hope this is useful.
Rod Downes