As someone who is stuck (not for much longer though!) with a fairly heavy, slow laptop, my iPad has been a lifesaver. I use it for textbooks, emails and web browsing. While I’m on the go it does just about everything I need to faster and in a much lighter package.
It does depend on your situation though, if you have a light, speedy laptop it might not be as necessary.
I consistently go around two days before I need to charge mine. Mostly use it for light browsing, emails, texts/calls and listening to music (locally stored). Most days I’m usually connected to WiFi about 85% of the time with LTE for 15%.
On more LTE heavy days I get easily a day, usually a day and a half.