Aperture resets when camera has been turned off

[Jnob]

Hi!

I’ve got some lenses with and some without aperture rings. When the lens does not have an aperture ring, such as the old 27mm, my camera decides I always want to start with an aperture of f7.1. When I changed the aperture, let’s say f4, but then turn off the camera and on, the aperture is back to the f7.1. It’s very annoying to keep my camera on and drain the battery, or have to change the aperture back every time. I shoot in aperture priority. Which setting do I have to change? Or is my internal battery faulty (I read that resetting when turned off has something to do with the internal battery?)?

Thank you!