A nickel-metal hydride battery, also known as NiMH, is a secondary cell. They are used in cameras and other electronic devices. They come in a few sizes; AA is the most common. They do not contain toxic chemicals like the nickel cadmium battery does. They work by the oxidation of hydrides, such as lanthanum hydride, by nickel(III) oxide. Older ones die quickly when they are not used, but newer ones are made to hold a charge. They have longer shelf life and are more durable than the lithium-ion battery, but are not as powerful for their size, although the best Ni-MH batteries are very close. They used to be more expensive than nickel cadmium batteries, but now the cost is similar.