Laptop vs windows tablet

Hi. I have 500 to spend and looking for either windows tablet or laptop. New or second hand it doesn't matter.

We have pc's in campus library although it some times gets crowded and there might not be enough stations for everyone. I would like to have my own portable workstation - to work in my time between lectures.

I does not have to be powerful ,I have powerful desktop at home for stuff that needs decent pc. All I need it for just enough to run multiple office windows without any lag. I think I might use it for reading ebooks, instead of recommended text books. I want minimum 12 inch screen and decent battery life to see comfortably what I am doing. If its laptop i pretty much decided on 13"-14" screen size.

I like laptop because they are more robust and powerful than equivalently priced tablets. But they are also much heavier and they batteries dont last long.

Tablets are much lighter, battery life better. Better at reading text from. But they are so fragile... Also most of the time keyboard is separate purchase and physical keyboard is must to me with tablet(typing assignments),etc.

I like Microsoft Surface, but when you add keyboard to price even used models claims over 500 mark.
For laptops I really like and heard only good things about Lenovo Thinkpads. They also very well priced in second hand market.