Smart Fortwo Alarm Failure Due to Auxiliary Battery Issue

Having experienced a similar battery problem with my Smart Forfour electric from 2017, I can relate to this issue. The auxiliary battery failure is a known concern in these models, particularly affecting the alarm system functionality. When my alarm system failed, the initial battery check revealed the auxiliary battery had degraded beyond its useful life. The auxiliary battery specifically powers the alarm system when the main car battery is disconnected, providing that extra layer of security. The repair process required accessing the auxiliary battery compartment, which is separate from the main car battery. A voltage test confirmed the battery signal was weak, indicating cell deterioration. The replacement took about an hour at the workshop, including system reset and testing. This is generally not a serious issue, but leaving it unaddressed can lead to complete alarm system failure and potentially drain the main car battery. The system needs to be properly coded after the new auxiliary battery installation to ensure all alarm functions work correctly. Worth noting that when these batteries start failing, they often trigger multiple error messages and can cause intermittent alarm activation. Getting it fixed sooner rather than later prevents these inconveniences.

Thanks for sharing your experience with the auxiliary battery replacement. My Smart Fortwo had the exact same electrical issue last year. The car alarm kept going off out of nowhere and the system diagnosis showed similar error codes. I ended up replacing both batteries since the main car battery was also showing signs of wear. How much did the repair end up costing you? Have you had any recurring electrical issues since the battery replacement? Just want to make sure the fix was permanent and not just temporary like some car alarm problems can be.

Since getting the auxiliary battery replaced at the shop, the electrical system has been running perfectly. The battery alarm error message cleared up right after the repair and hasnt returned. They charged 330€ total for diagnosing and fixing the battery discharged condition, which included the new battery and reprogramming the alarm system. No recurring issues at all with the car alarm or electrical system in the past months. The technician explained that as these auxiliary batteries age, they start causing various warning signals and unusual alarm triggers. Getting both batteries replaced at once was definitely the right call, it prevents cascading electrical problems that could end up being more expensive. The Additional battery alarm system defective warning is completely gone now. For anyone else facing similar symptoms, having a proper diagnosis done early helps avoid more complicated electrical repairs down the line.

After reading through the responses, I wanted to share how my repair experience turned out. I took the car to my regular shop last week for the electrical issue. The system diagnosis confirmed what others mentioned, the auxiliary battery was completely dead and triggering the car alarm out of nowhere. The mechanic found the voltage was way below normal and recommended replacing both batteries. Since the main battery was already 4 years old, I agreed. The entire job including parts and labor came to 295€, which seemed fair given the work involved. The repair took about 2 hours total while they tested the electrical system and reprogrammed everything. So far the alarm system is working perfectly with no error messages or unusual triggers. The battery problem seems completely resolved and the car starts much better now too. Looking back, I'm glad I addressed this early before it could cause more extensive electrical damage. The mechanic said these auxiliary battery failures are pretty common on these models after about 8-10 years of use.