MacBook Pro – Is It Normal to Run Hotter When Plugged In?

Some obvious causes:

1. Need to wait 30 to 60 seconds for the SMC to read the battery and decide what to do
2. check for pencil lead/debris on the mac end of the magsafe
3. check for pins stuck down on the magsafe cord end of things
4. The SMC needs to be reset on the Mac
5. The battery, all adapter or charging circuitry itself is faulty or detecting something that causes a pause and the mac might need service. (This is exactly what your mac will do if it needs an 85 watt adapter but you've somehow gotten your "friend's" 65 watt adapter - if your adapter isn't putting out enough power, the mac can only run and not support the CPU/GPU load as well as the charging circuitry. Similarly, if the battery is drawing more than designed, the mac will prefer to run than charge and tells you this in the not charging message.)

Due to the way batteries work, they can be out of tolerance / spec at only a specific portion of the entire voltage range. The sensors will correctly detect “good battery” until you reach that one point where the voltage drops too fast and shows aging or a problem with the cells.

Do a calibration run at your earliest convenience if your battery doesn’t continuously self regulate and calibrate. Next, think about a visit to the genius bar or other Apple Support / service desk if the problem continues. Take your wall adapter with you when you go as it can be checked with the mac together.

I believe that it is common for the CPU to reach 90°C under heavy load. However a simple video should not bump an i5 into that region. Depending on the footage and format you are playing back you might want to try a different player (vlc mplayerX). If you are playing back flash HD videos in your browser (especially multiple streams simultaneously), that behavior might be common (due to the bad flash performance on os x).

So much for the software.

Secondly you should take care of the outer temperature (e.g.is your computer in a very hot room) and even more importantly where your notebook is placed. e.g. does it sit on a carpet or any other good insulating soft cushiony surface that prevents heat from leaving your computer.

Thirdly you might want to take a look in the activity monitor and see whats using your cpu. (Maybe some background application e.g. spotlight indexing new pdfs)