How to maximise the battery life of my iPad

I'm trying to maximize the battery life of my iPad. Is there some way to set it so that it locks after 5 minutes of no use, and completely shut down the iPad, or put the iPad in lower power mode, if it hasn't been unlocked for 4 hours?

Sometimes I may go 24-48 hours without using the iPad, and I'd like it to just shut down and not drain battery, rather that go grab it and find out it's dead.

[Re-Titled By Moderator]