Hello,
I have a 09 s60 awd, last summer (Arizona) I noticed that my interior lights were not turning off when the car was off after locking. To prevent a dead battery I unplugged the negative terminal. Every now and then that summer my dash and electronics in the car would go out (no power windows, ac, dash off, rear lights off), the radio would still work. I had an SRS error message show up around this time. As the temp cooled down the problem went away. Now back to summer I have run into this issue again, but cannot get any electronics to come back. Even after leaving the car in the garage with the negative terminal off for a day. I had the battery checked and it is fine, auto zone said the alternator was going bad. I charged up the battery before going to auto zone. After doing that I did get a check engine light that would stay lite (turns off after the car is on), prior it would light and go off in under a second. Doing research I could not find a link to a bad alternator with my symptoms. I initially thought it was the DIM but also started to think the ECU was overheating. I tried known resets. Checked fuses and everything is in working order. I am at a loss for what could be wrong, I would assume it is electrical. The car drives great, no higher revving, or sluggish acceleration. The car would turn over slower when the problem started last summer. I am taking it into a volvo specialist this coming Monday, but would like to see if anyone has any suggestions or ideas.

TL;DR: No electronics or gauges work, cannot like symptoms to problem.