Battery life is a really big deal. Recent surveys from IDC and The Guardian suggest that it's the number one concern among smartphone buyers. We all hate it when our phone doesn't make it through the day, but our buying habits show we're not willing to lug around thick, heavy, costly phones with bigger batteries. We've provided tips on how to boost your phone's battery life, but to make a serious difference, we need deep-down changes to the Android operating system. Android L aims to give us that big battery life boost through a series of enhancements Google calls "Project Volta."
Similar to Project Butter (Android 4.1's improvements to get everything running at 60 frames per second) and Project Svelte (Android 4.4's push to make Android run well on devices with only 512MB of RAM), Project Volta is not just a singular change. It's a blanket term for a suite of enhancements that aim to significantly boost your smartphone's battery life.
As part of building Android L, Google created a tool called Battery Historian that allows developers to visualize exactly what's using your phone's battery, to what extent, and at what time. This helped the company make a bunch of under-the-hood changes to Android that lowers its overall battery consumption, and it will help developers profile the energy use of their apps.
The ART runtime
Android L brings with it the new ART runtime environment. While it's currently available to test in Android 4.4, the version in Android L is more advanced. Google's promising a big performance boost to apps in addition to lots of new features like support for 64-bit processors and apps, but there's an impact on battery life, too.
The current runtime environment, called Dalvik, compiles code every time an app is run (this is called "just-in-time" compiling). ART compiles and optimizes the app's code once "ahead-of-time", meaning less processor time spent compiling and thus less power use. There's a lot of technical stuff in ART (like vastly improved garbage collection) that makes it faster and more efficient than Dalvik, all of which translates into better battery life.
Battery Saver mode
No matter how long your battery lasts, there will be those moments when it gets dangerously low, and stuck away from a plug. Phone manufacturers like Samsung and HTC have addressed this with special low-power battery saver modes to their phones, and now, Google is building it into Android itself.
When your battery drops beneath a certain threshold (the default is 15%, but you can adjust it in 5% increments), Battery Saver will lower the processor's speed, reduce animations, dim the screen, and reduce radio usage. The idea is to get power down low enough to get you to the next charge without making your phone useless. In the Android L developer preview, the feature really makes everything feel like molasses, but it's better than running out of juice.
Google's upcoming Android OS adds a new feature for developers called the JobScheduler API. It lets developers define specific background tasks that should happen when certain conditions are met. For example, an app could say "wait to sync until the phone is plugged in" or "grab this data every hour when connected to Wi-Fi." Developers have been able to do this kind of stuff themselves, but they have to essentially wake up the device to determine its state.
With the JobScheduler API, developers can define the conditions for their apps to do something in the background, and the Android system will determine when the conditions are met, batch together all the necessary tasks, and perform them at once.
Does Project Volta work?
Recently, Ars Technica performed its standard battery tests on a Nexus 5 running both Android 4.4 and the developer preview of Android L, and the results were impressive. The test involves taking a fully charged phone (with Battery Saver disabled), setting the brightness to 200 nits, and making it run a script to refresh the same set of web pages over Wi-Fi, every 15 seconds, until the battery runs out.
The developer preview of Android L lasted a whopping 36 percent longer than Android 4.4. That's another two hours of screen-on browsing time! It's hard to say exactly how this will translate to your own phone, loaded with a variety of different apps running the final version of Android L, but these early results are incredibly encouraging.