A power extender is a back-up power source that can be used to charge a cell phone, MP3 player, or other device. Power extenders are also available for laptops. These devices are often cheaper than extra laptop batteries and offer a few hours of extra power. Power extenders are important to remember on long flights, train rides, and other times when your batteries are likely to run out of power. If you�re traveling out of the country and don�t have an International adapter, a power extender can be especially useful. While these devices may offer a limited amount of power, it�ll be enough to tide you over until you can find the right adapter.