Use Power Saving Mode
While we're talking about battery life, there's a way to save even 20% to last hours on end. It's called Ultra Power Saving Mode. Navigate to the same battery area as mentioned above and enable this. It puts the phone into a black and white state, disables many behind the scenes things, and makes the phone act more like a dumbphone from 2003. However, the battery can last for hours in case of an emergency.
Go to settings > system > battery > Ultra Power Savings mode and turn it on, then read all about it to see how great it can be.
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