Despite their various bells and whistles, these apps employ one basic technique to achieve their goal: They kill apps and background processes that don't directly affect the task at hand. The theory is simple: Why let Google Maps pinpoint your location or Google Calendar sync your appointments or Facebook update your feed while you're trying to do something completely unrelated?
These apps aren't quite as effective as Lollipop's complete runtime overhaul, but they make a noticeable difference, especially for devices with a limited amount of RAM. Some, like CCleaner (free), clean your device's cache, browsing history, and other temporary data to free up both RAM and ROM; others, like the excellent Greenify (free), DU Speed Booster (free), and Clean Master (free), add tricks like CPU temperature management and even antivirus protection.
DU Speed Booster Android appDU Speed Booster adds antivirus protection to its array of performance features for speeding up your Android device.
Like all the apps we've looked at, performance-boosting software is largely dependent on your device and your usage habits. The Nexus 6, for example, with its top-shelf Snapdragon processor and 3GB of RAM, probably wouldn't benefit as much as a Galaxy Nexus would with its aging processor and limited 1GB of memory, simply due to its higher performance capacity. However, for aging devices, the math behind these apps is simple: The more background processes you're running, the less RAM you have to devote to other, more important tasks.
The bottom line on battery and performance management apps
Despite the improvements these apps provide, the best thing you can do to tune up your aging hardware is to simply upgrade it to the latest version of Android wherever possible. But for devices that don't yet have the luxury, lackluster battery life and performance aren't unavoidable. While claims of wild improvements and a completely rejuvenated device are largely inflated, these apps aren't entirely bunk. These solutions use tried-and-true methods, some of which have even been incorporated directly into the latest iteration of Android, to achieve tangible improvements — they're worth a download, even if only to hold your device over until core changes can take effect.
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