To maintain a constant supply of energy simply refill as the water evaporates, typically every 2 to 3 months. The H2O battery has a minimum continuous life of at least 2 years. In addition to this, the H2O battery (unlike all other conventional batteries) can be stored in its dry state indefinitely and can be left to dry out at any time during its life and its life extended indefinitely. As all the components of the H2O battery are recyclable, the benefits over traditional batteries are countless. Unlike conventional solar powered calculators the H2O Compact Calculator can be used in all light conditions... no more fading displays at that critical moment. The H2O batteries are easy to refill and can provide constant power for up to 3 months with just a few drops of water. Dimensions: 75 x 18 x 110 mm