I need to set up a Q&D no-break power supply for a small datalogger, 5V supply at 20mA or so. The easiest approach is to use a 12V plugpack and a 9V dry cell, commoned via silicon diodes, feeding a 78L05. I'm just wondering whether the very small backfeed current into the dry cell through the back biased diode might have adverse effects on cell capacity over an extended period. The supply has to hold up for months, with breaks potentially up to an hour or two.
Any experience?