If your laptop battery fails or no longer holds a sufficient charge, you can easily replace it. But as long as it is working fine then you don't need to replace it.

You can't you can only do that on PC's

i agree

You should go to a expert for that. I strongly do not recommend taking apart your laptop

Some laptop microphones have internal errors with them, so you should replace them. You can replace them at BestBuy or any other electronic store for a lesser price.