Everyone loves Doze Mode in Android Marshmallow, but Sony has been doing something similar for a long time. They called it "Stamina," and it has been around for 3 years. Stamina mode was removed in the latest Xperia Marshmallow update, but it could be making a return. Sony Japan says Stamina mode will return in April. We don't know how Sony will differentiate Stamina from Doze. It will be interesting to see how the two co-exist on a phone.