Im wondering if theres a difference in performance if i have it connected to the charger vs being used with battery only because there a messege that appears when disconnecting something about graphics card bbla bla bla
Yes definitely. Depending on how you have your machine set up it will either throttle back the performance on your Nvidia/AMD card or more likely switch to the Intel integrated graphics. This is to conserve power.
It will boot up faster. But times will depend on how many services are being loaded at startup. Also if you are using windows, the system automatically calculates a page swapping allocation which will affect performance. Ideally you should always maintain a minimum of 20% HDD availability to enjoy a decent user experience.
You can set it up to where there is no difference, but don't be surprised if your in the middle of a game and your PC shuts off due to low battery. High performance settings will eat through your battery like it doesn't exist.