Is it possible to change the battery in a Citroen C4 with a Carly adapter?

You can certainly change the battery yourself if you're comfortable with it. Just make sure you have the correct replacement battery and follow the manufacturer's instructions carefully. However, the rough engine running might be a separate issue. It could be due to a variety of reasons like spark plugs, fuel injectors, or even the air filter. I would recommend getting a diagnostic scan with your Carly adapter to pinpoint the issue. After replacing the battery and running the diagnostic, let us know how your car is performing. Do you have any other questions?