The technology relates to a capacity indicator for use with a battery. One aspect of the technology provides an improved activation circuit for a capacity indicator that is easier to use and less prone to false alarms. A further aspect of the technology provides an improved indicator which is able to indicate battery capacity without requiring the use of expensive battery labels such as thermochromic strip. A further aspect of the technology provides a capacity determination circuit which is housed within a battery and which is able to provide a more accurate indication of battery capacity.