Intermittent Starting Problem
 

My 2000 S80 has an intermittent starting problem. Once or twice a week, the battery will be too low in the morning to start, engine doesn't turn over, just clicks. Other mornings it starts normally. After jump starting, it works normally for several days. My independent mechanic and the local dealer have both spent hours trying to trace down any problem but can't find anything. Battery is fine, charging system normal, no unusual power drains.

Some possible clues: alarm goes off for no apparent reason and doors lock by themselves; these may be the result of low battery, voltage-starved computers do oddball things. Also, after each episode, the clock needs to be reset, and the door lock buttons and the sunroof switch won't work until the car has been turned off and on a couple of times; again these could be effects, not causes.

Any suggestions?