Having Flash installed can cut battery runtime considerably — as much as 33 percent in our testing. With a handful of websites loaded in Safari, Flash-based ads kept the CPU running far more than seemed necessary, and the best time I recorded with Flash installed was just 4 hours. After deleting Flash, however, the MacBook Air ran for 6:02 — with the exact same set of websites reloaded in Safari, and with static ads replacing the CPU-sucking Flash versions.

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