BGR writes that Pokémon Go developer Niantic has been addressing fans concerns about recent developments in the game, including the fact that it removed the Battery Saver mode in the most recent update. Prior to its removal, this mode worked by automatically dimming when you put your phone upside down in your pocket when playing the game, thus saving battery life. Well, that was the theory, anyway. While many Trainers found it useful and were disappointed at the disappearance of the Battery Saver mode, others found that it caused their screen to freeze.
And it seems that this very glitchyness was what caused Niantic to remove the mode for now, but they do have plans to bring it back, hopefully with all bugs removed.
So that’s good news for Trainers, then, if not for portable battery charger manufacturers!
Source: Pokemon Go’s long-lost battery saver mode is making a comeback on iOS