Peugeot 308 start stop problem

That does sound like a battery issue, especially given the hybrid system's reliance on a healthy battery for start-stop functionality. When the battery voltage drops too low, the system will often disable itself and throw errors like you're seeing. Has the car been sitting unused for extended periods, or have you noticed any other electrical issues, such as slow cranking during engine start or dimming headlights at idle? These could point to a discharged or failing battery.

Thanks for the quick reply. I haven't noticed slow cranking, but the car does sit for a few days at a time sometimes. Could a simple recharge potentially resolve the issue, or am I likely looking at a full battery replacement?

A recharge might help temporarily, but if the battery has been repeatedly deeply discharged, it's likely sustained some damage. The hybrid system puts a lot of stress on the 12V battery, and they tend to degrade faster than in a conventional car. Given the symptoms and the potential for further issues, I'd recommend having a workshop perform a battery test using a proper diagnostic tool. They can determine the battery's state of health and advise on the best course of action. Continuing to operate with a weak battery can also put extra strain on the starter motor and other components.

Understood, I appreciate the detailed explanation. I took it to a workshop, and they confirmed the battery was heavily discharged and defective. Replacement cost me 290€, but the start-stop system is now working perfectly. Thanks again for your help!