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Dizziness and fainting after changing the battery of the pacemaker indicates malfunctioning of the pacemaker. You should discuss these symptoms with your cardiologist as you may need to get the status of the pacemaker checked.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care.