Weight Weenies

Basically, my powertap has stopped working after new batteries have been placed in (pro+) I've done all thing suggested to do unless there are any more that are more unknown.

seems like it needs replacing/repairing which isn't cheap from what i have been told. but i do have a Quarq MTB one, so can I use this on my road bike if i switch the rings to larger ones (80mm/120bcd).

Is this possible, aslong as i can get it re calibrated via their app and the correct procedure to do so.

or any suggestions on what could be wrong with the PT.

Dumb question but.....
Its the old 2 hearing aid battery type? have you put the batteries in the wrong way round?
It is possible...

or check to see if your new batteries are any good?

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If it's not something you can fix, Saris has a good warranty. If it's out of warranty, then they have a good repair program that's not too expensive.

On your second question, you may have a chain line issue with the MTB crank.