when changing the battery, what voltage should the power saver
be? on 2005 BMW 525i

Rookie cbe0621eac06868b3efe0d8d1d3611e23c60d3114864ea2ec19a68cfbd3eebab
there is a choice between a 9v battery saver and a 12 volt
battery saver.
(1) Answer
A 9v power saver will be fine for keeping your radio and security settings. If you are planning on replacing batteries for a living then invest in the 12v.