By default, mobile devices are set to high performance mode. This is good in that your device will always be available quite quickly for example for when your lid is closed. The bad news is that your battery will drain quite quickly when not plugged in. There are a few things you can change to make your battery last further.
Battery saver
The first one being to turn on “Battery saver”. To do this. select the Start ⊞ button, and then select Settings > System > Battery . Under the “Battery saver” heading, check the box next to “Turn battery saver on automatically if my battery falls below:”, then drag the slider along to the desired percentage. I would recommend keeping it quite high (80%) and see how the performance is.
Change what happens when you close the lid
Another good option would be to change what happens when you close the lid/fold the keyboard over. By default this puts your device to sleep, which still uses battery. Another option would be to hibernate the computer when you close the lid. This saves the state your machine is, then turns it off so it’s not using the battery. When you turn it back on, it will restore the state you left it in. To do this, select the Start ⊞ button, and then select Settings > System > Power & sleep > Additional power settings > Choose what closing the lid does.
For further reading, see Microsoft’s Battery saving tips here.