Learn English – A single word or phrase for something that necessarily causes both harm and benefit

You could call this a double-edged sword. It can be used both for good and bad.

Battery hog is a good expression. It would be instantly understood in the tech field. By way of analogy, we call CPU-intesive apps CPU hogs, as in Chrome could be a huge CPU hog.

Here's an example from CNet:

GPS is a huge battery hog, as it harnesses data from the phone's GPS chip, cell phone towers, and Wi-Fi hotspots to find your location

(http://www.cnet.com/how-to/how-to-get-better-battery-life-on-android/)

Or you can simply say battery drainer:

Surprisingly, the Wal-Mart (WMT) app is the top battery drainer among U.S. Android users in this category.

(http://money.cnn.com/2015/06/03/technology/battery-draining-apps/)

The adjective battery-intensive could work as well:

What are the most battery intensive apps?

(http://forums.macrumors.com/threads/what-are-the-most-battery-intensive-apps.1097790/)

Edit: These may not be very common, but they still, I think, deserve a mention:

battery killer:

No, GPSD is not the battery-killer on your Android!

juice-killer:

Can somebody help me figure out what is draining my battery so much? - springtomize is definitely a juice killer...

juice-drainer:

The big Note 4 big screen will likely be a real battery juice drainer.