There have been reports going around all the various social media networks you can think of that downloading your local maps on Google Maps will save some battery life when you’re out hunting Snorlaxes and Koffings in Pokémon Go. Sadly, that’s not the case, and a Google engineer has confirmed it.
The idea is that since Pokémon GO is constantly accessing maps via the Google Maps API, downloading your local maps would save you battery life by decreasing the amount of data and number of data requests your phone would have to make to the maps server for information. It’s a neat idea! But it’s just an idea, and for those who have said it works, it seems to just be a placebo effect.
@taybenlor short answer: no. long answer: nooooo
— Sam Thorogood (@samthor) July 11, 2016
In short, regardless of whether you have those maps downloaded, Pokémon GO isn’t accessing that data. The idea could, in theory, be a way for developer Niantic to help its users save a bit of data, though. If the game application were updated to allow offline map storing, it could save a few megs of data and a few minutes of battery life, but until Niantic implements such a feature, we won’t know.