Android Marshmallow has proven that it can extend the battery life of smartphones with its doze feature, but Android Wear devices will receive the same benefit once they are updated to Android 6.0. It's unknown how much longer batteries on the smartwatches will last with the new software build, but it won't likely be a game changer since the doze functionality only kicks in if the device doesn't move for a long period of time - something that's quite infrequent for a smartwatch since it's attached to your wrist most of the day.