Even so, the modern mirrorless systems nowadays have a decent battery lifetime, that gets you through the day, it can be yours that you get into situations where you must be economical with the remaining energy. I would like to give you a few tips and hand that will enable you to continue working as long as possible.
Use the display not the viewfinder!
Even though the back display of your camera is much bigger than the display in your electronic viewfinder, it needs much less energy. This sounds weird but is logical. The viewfinder has much more pixel and as switching pixels needs energy the viewfinder needs more energy. Besides, the refresh rate of the viewfinder is much higher than the one at the back display. This needs also more energy.
Reduce display brightness!
Once you are using the back display you could optimise the setting. By reducing the brightness of the display you can save additional energy and extend battery life.
Switch of image stabilisation!
Olympus OM-D camera does have fantastic image stabilisation, but to be able to correct movements it needs energy. In case your battery life is at the end you have to decide whether you would still use the image stabilisation or not, but you can shoot some more images.
Switch off Autofocus!
Even though that manual focus in a modern camera is realised by electro motors, you are able to save energy in case you switch off the autofocus. Especially when you are shooting slow-moving object as you just have to set the focus once. The autofocus on the other side is moving the motor every time you half-press the release button. Alternatively, you could use the back button focus method, which uses the AEL/AFL button to activate focus.
Keep your batteries warm!
The capacity of batteries highly depends on the temperature. Working in cold conditions the battery life is much shorter than usual. Therefore I have always one battery close to my body to keep it warm, mostly in my pocket. In case the battery in-camera is dying I can use the one in my pocket.