A measure of the amount of time a watch will run after being fully powered or wound, with no additional power input. Normally, this means when a mechanical watch is fully wound or a quartz watch has a brand new battery. Many modern mechanical watches have a power reserve of 40 hours. Power reserve also applies to battery-less quartz watches, which may have power reserves from 40 hours to 6 months. On battery-operated quartz watches, the term is sometimes used to refer to the expected battery life--typically 12 to 32 months.