Macbook pro 2011- High CPU usage after troubleshooting/clean install

I have a Macbook pro 2011 version running 10.6.8 that has all a sudden started running extremely slow. I checked the activity monitor utility and it shows the kernel_task is running at ~%300. The RAM usage (4gb) seems stable, HDD disk shows some spikes but seems stable as well. Eventually if I let it sit for a bit, kernel_task will subside but even opening a simple browser will cause the system to slow down and hang up again but not freeze.

I have run Onxy and all the automated features, reset the SMC and NVRAM, tried a clean install using the disks that came with the system and still have the same issues without even doing a back up of my time machine files, run Onyx again after the clean install, boot into safe mode (seems to help a little bit but still really high CPU usage), used the Apple Hardware Test (No issues), removing battery connector temporarily ( the battery currently does not charge and needs to be kept on charge for the MAC to stay on),

Are there any other troubleshooting tips I have not tried or advice you all might have?

I was thinking of swapping out the HDD and ram but I am wondering if that will help at all since the issue is high CPU usage not HDD or RAM use. Do you think it will still help.

Any suggestion at all will be appreciated!