Silver-zinc battery is an important energy equipment in aviation and aerospace field. It is an urgent problem to use the test data to assess battery reliability after the battery is activated. A degradation model of voltage of the standby silver-zinc battery was established based on Wiener process. The reliability function of the battery was given. The maximum likelihood estimation method was used to estimate the unknown parameters of presented model. By using the discharge data of the standby battery which was activated, the reliability of the batch of the battery was evaluated out, with the conclusion that the standby life of activated battery is 51. 95 hours on the condition that the reliability is 0. 95.