Smart Fortwo Battery Issues Causing Multiple Failures

I dealt with a very similar electrical system problem on my 2016 Smart Forfour last winter. From someone with decent experience working on cars, the symptoms you describe match what I encountered, a discharged battery that kept draining despite being fully charged. After seeing multiple error messages and experiencing those weak, flickering lights, I took it to a workshop. They diagnosed a faulty battery sensor that was incorrectly reporting the battery state to the car computer, causing constant battery drain. The repair involved replacing the sensor and recalibrating the electrical system. Total cost was 315€, but it completely resolved all those electrical gremlins. Before jumping to conclusions though, could you share: How old is your current battery? Does the battery warning light stay on while driving? Have you noticed any correlation between these issues and using specific electrical features? Did you have any recent electrical work done on the car? This information would help determine if youre dealing with the same battery sensor issue or potentially something else in the electrical system.

Thanks for sharing that insight. My car has 195701 KM and had its last service 4 months ago. The battery is actually quite new, replaced just 8 months ago. However, I noticed corrosion building up on the battery terminals, which might explain the battery drain issues Im experiencing. The battery warning light flickers occasionally but doesnt stay on consistently. No recent electrical work has been done. Given these symptoms and the fact that even a new car battery is showing problems, Im beginning to suspect the alternator might not be charging properly. When checking the battery terminals yesterday, I measured only 13.2V while the engine was running, which seems a bit low.

Thanks for providing those additional details about your Smart Fortwo. The voltage reading of 13.2V while running is indeed lower than optimal, a healthy charging system should show around 13.8-14.2V. Your suspicion about the alternator could be right on point. When I had my Smart going through similar issues, I initially focused on the dead battery symptoms, but it turned out the alternator wasnt providing sufficient charge. The corrosion you mentioned on the battery terminals definitely wont help the charging situation either. Here is what worked in my case: First cleaned the battery terminals thoroughly to remove all corrosion, Had the alternator tested, which confirmed it was underperforming, Replaced the alternator (cost was around 450€ including labor), Also replaced the serpentine belt since it was showing wear After these repairs, the electrical system returned to normal, no more flickering lights, error messages cleared up, and the battery maintained a proper charge. The voltage reading went up to 14.1V while running. Given your identical symptoms and that low voltage reading, I strongly recommend getting your alternator tested. Even a new car battery wont perform properly if its not being charged correctly by the alternator.

Your car battery situation definitely sounds concerning. Thanks for the detailed solution, I really appreciate learning about your similar experience with the alternator and charging system issues. Based on the voltage readings you shared, Im going to schedule a full electrical system check at my local shop this week. The combination of battery drain symptoms and that 13.2V reading while running really points to charging problems rather than just battery failure. Ill make sure they thoroughly clean those corroded terminals and test the alternator output. If it does turn out to be the alternator, the 450€ repair cost you mentioned helps set my expectations. Its reassuring to know that replacing it resolved all those electrical gremlins in your case, the flickering lights and error messages have been driving me crazy. Ill post an update once I get it diagnosed and repaired. For now, Im just glad to have a clearer direction on what to look for rather than just assuming its another discharged battery issue.