Hi Dennis

If you check the schematic of my 80C535-mainboard you will find the way how I use a 3.6 volt battery to keep the contents of a SRAM 62256 up-to-date. I have the information from the creator of the BPlus-board of the Dutch Forth-Usergroup. I use a 74HCT00 to get the signals right. Special care should be taken where the + of the battery is connected to. I use two BAT85-diodes also.

http://members.home.nl/bzijlstra