Now that Sony is rolling out Marshmallow software to the list of devices it stated that they would be supporting, like the Xperia Z3, Xperia Z3 Compact, Xperia Z5 series, and more, those who use such devices may have ended up noticing a very once-familiar Sony-specific feature is gone - Stamina Mode. If you've used an Xperia device for any length of time, Stamina Mode was like the bread and butter of battery savings and this is something you likely come to appreciate over time. With it enabled, users could extend the life of their battery quite a bit as the feature would turn off functionality of certain apps or other features to preserve battery life a little longer. Sony seems to be reintroducing Stamina Mode in the latest version of the Marshmallow beta.
Although users on Marshmallow may now have Doze Mode, that doesn't necessarily make it a replacement for Stamina Mode, especially if you've been used to keeping it enabled for the longest time. The slight letdown here is that this is only available in the beta at the moment, so until Sony pushes another small Marshmallow update to reintroduce it to everyone who is currently on Android 6.0, you'll have to stick with Doze and perhaps watching things a little more carefully in terms of battery consumption.
Back in April, Sony acknowledged that Stamina Mode was indeed gone from the Marshmallow version of their software, but they also confirmed that Stamina Mode would return at some point down the road. That process appears to have been initiated and as soon as they have tested it with users in the beta it may not be too long before they send out the update that adds Stamina Mode back to non-beta devices. If users will really want to dial things back, Ultra Stamina Mode will be coming back alongside regular Stamina Mode as well, which will disable mostly any service that runs on the device besides the basics such as phone, messaging, camera, and contacts. There also appears to be an option included with Stamina Mode in the beta which allows you to set it to turn on after reaching 15 percent battery.