My Macbook CPU runs at 75C and the ran runs full speed when the battery is connected to the computer - if I remove the battery the CPU temperature falls to 50C or lower and the fan speed returns to 1800rpm. Plug the battery back in and the CPU reaches 75C and the fan goes back to high speed. This situation happens whether i'm logged in or not - I can sit at the login screen, remove the battery and the CPU/fan calm down. I have reset the PRAM by disconnecting the power and battery, holding the power-on button for 5 seconds, etc. no change in behavior. I'm not sure how to resolve this. This macbook is one of the 2GHz Core 2 Duo models purchased April 2007. This weird behavior started happening today - i've been using the machine quite a bit since I got it (new from the Apple store). I checked the battery health with iStat - it shows health is 93%, 51 cycles and charged 100%. Running Leopard, 10.5.3. Any ideas? Help! -- I booted into Tiger using my iDefrag DVD and the CPU/fan behave normally, with the battery installed. I haven't tried booting my Leopard DVD but I have a hunch that the CPU/fan will behave normally with the install disc as well. Before I waste 2 days of my life re-installing the OS and all my applications, data, files, etc. does anyone have any suggestions how to get around this? It's REALLY going to make me mad if I have to rebuild the whole environment because of a rogue bit that's been flipped in a config file in the OS.