Afternoon all - been a while!

My wifes 2005 R50 Cooper has developed a wee "issue" with the CVT box. Around town / slow speeds [IE <30mph] it seems to not step up/down the range and instead leaves the car revving up about 4k rpm? Can't tell if this is a CVT or Throttle issue or both? Faster speeds there's no issue and makes no diff if in D or SD.

Any thoughts?

As a wee aside [sure I read it somewhere] is there any chance this could be linked to a weak battery at all? It hasn't done a lot of mileage this year and the battery isn't the strongest requiring a top up quite regularly now.

Cheers :)