For each Android release, Google likes to have a "Project" that picks an area of weakness and focuses on tuning the whole OS to fix it. In Jelly Bean we had Project Butter, a concerted effort to make Android's UI animations run at 60fps. In KitKat there was Project Svelte, which aimed to get the OS running on only 512MB of RAM. Now in Android L we have "Project Volta," an attempt to boost the battery life of Android devices. Like the projects that came before it, Volta is a wide-ranging effort that touches many different parts of the OS.

Google did some testing and found that waking a device up for one second burns two minutes of standby time. This isn't just turning the screen on—it also means an app waking the processor and modem to check for updates. To cut down on this battery burn, Android L has a new "JobScheduler" API that allows the OS to batch up unimportant app requests like database cleanup and log uploading. Developers can also request that housekeeping functions be delayed until the device is plugged in. Further, the OS will not wake the device up for a network task when there is no network connectivity.

Google also made an enhanced battery stat tracker called "Battery Historian." The tool added a ton of new power-tracking capabilities and allowed the company to visualize all that data in a pretty chart. Better analytics gave Google more insight into what was using all that power, which allowed it to tweak things all over the OS for better battery life.

There's the switch from Dalvik to ART, a faster virtual machine that compiles apps once instead of every time they are run. ART is also generally faster and more efficient than Dalvik, which means less time spent processing and less power usage.

That all sounds great, but does Project Volta actually work? We decided to find out by running our review battery test. Just like in our reviews, we were as scientific as possible. We did the test on a single device to remove variances in battery, which meant flashing to 4.4.4, signing in, updating apps, charging up, running the test, and then flashing the same device to the L preview. Our battery test keeps the screen on and automatically loads webpages over Wi-Fi every 15 seconds until the battery dies. For each run, the screen brightness was set to 200 cd/m2, as verified by a colorimeter, and for consistency, we averaged two runs each. The results?

Thirty-six percent more battery life. Installing the L preview on our Nexus 5 gave us two extra hours of runtime. These tests were done on a beat up, daily-driver phone, so the final numbers aren't necessarily indicative of what the L preview could achieve on a new device. It's the difference that matters.

Android L also has a "battery saver" feature that lowers the device performance and cuts the background data and screen brightness when the device hits 15-percent battery, but we disabled this feature for our tests. We like to have our devices at full power, and we don't want a hyper-aggressive phone-crippling feature messing with our results. Presumably, you could gain even more runtime by turning the battery saver on. This test is more about the general under-the-hood improvements that are running all the time.

This is just an early look at Android L's battery life. The current release is a "developer preview," but Google has already been able to make a meaningful difference in the runtime of L devices. Some of the new power-saving features, like the job scheduler, require app support, so there's probably room to improve not only in the OS but in Google's bundled apps, too. By the time the final version of L comes out, things could be even better. Google definitely looks to be on the right track.