Okay, a dead PRAM battery shouldn't be that much of a problem. Besides the obvious date & time issues associated with a dead battery, the other would be corruption of the PMU (Power Management Unit); a little computer within the computer that holds hardware settings in a cache. When the battery is dead, it may have some stray currents or under-volts that trigger the PMU, causing it to be corrupted. Kind of like throwing off a bean counter and making them start all over again. So I'd say that a dead battery is to consider, but not critical at this time.
If you do plan on replacing the thermal compound on everything, go right ahead. Use Arctic Silver type, since we trust it; you can get some online or Radio Shack now carries them for about $10 or $11 U.S. Dollars. While you are working under the hood, you can check to see that the CPU and chipset feel and look secure, not pulled away from the logic board due to overheating.
Looking at the temperature specs, the only one I'm concerned with is the processor bottom side @ about 140 degrees F. Can anyone else out there confirm that this is a normal F temp? It seems a tad bit high, although if it were about 160 to 180 or more, then I'd be really concerned. All the other temps look normal.
A bad video data cable (ribbon) going from the logic board to the LCD screen can and will eventually wear or short out, so replacing that might help. But the only way to tell it definitely needs to be done is if the display cuts out while you tilt the LCD full on open and nearly closed. The back-lighting will still be on, but the video signal will disappear and reappear again, once things settle down. A bad cable could send any short circuit signals backwards and screw things up, but I doubt that.
A bad inverter cable going from the bottom half of the PowerBook to the LCD screen can go bad, but when it does, causes the back-lighting to flicker while you open or close the display; similar to the video data cable mentioned above. The other symptom is no back-lighting but you can see the normal desktop, when you shine a flashlight into the front of the screen.
Software is up to date, RAM reseated, but Onyx crashed. Darn (somewhat). A permissions scan is less critical than if you were to spring clean the cache files, which the chipset and/or GPU require for fast storage of temporary info. The permissions simply tell the user, OS and others what privileges you are granted to each file and directory; whether or not you can read, write, modify or erase anything. You can try executing the daily, weekly, monthly scripts in the maintenance category and then move on to the cleaning category, where you can flush out all the cache files. Try that.
Do you have the install discs that came with that model PowerBook? If you do, there may be a disk containing the Apple Hardware Test (AHT). I would recommend booting that and running the tests to rule anything else out. Just a suggestion.
73s de Phreakout.