Google has apologised after Android phone users noticed that the battery saver setting was remotely activated last week without their consent.
The battery saver affects how often apps update and work in the background.
"This was an internal experiment to test battery-saving features that was mistakenly rolled out to more users than intended," the company said on Reddit.
"We have now rolled battery saver settings back to default. Please configure to your liking. Sorry for the confusion."