why is mail using 24% of my battery life and what is "background" activity?

[Ckar]

here is the screenshot:

compare mail with gmail, gmail is my main email app. why is mail taking so much battery life and how can i fix this?

 

[flashflooder]

It's probably downloading all your archived email messages. Does it every time I update to a new OS and takes a while to d/l 15 years' worth of emails.