Power outages may result in losing the settings of pool timers. But don’t worry, because timers like the Woods 50015WD Outdoor 7-Day Heavy-Duty Digital Plug-in Timer are equipped with self-charging batteries that take over as soon as the power’s cut. This helps to retain your original programming. With a mechanical device, although it stops working when no power is supplied, your settings are retained because the pins set around the dial don't reset themselves in case of a power outage.