Stagea Undervoltage Issue

Undervoltage issues in a vehicle like yours can stem from a few potential sources. The symptoms you've described, such as difficulty starting, system failures, and weak lights, are indeed indicative of a voltage drop. Have you had the battery voltage checked recently, especially under load? A healthy battery should maintain a voltage above 12.6 volts when the engine is off and around 13.7 to 14.7 volts when the engine is running. Also, when the voltage drops significantly during starting, it can point to a degraded battery that cannot supply the current that is needed to start the car. What voltage readings are you observing?

Thanks for the info! I haven't checked the exact voltages myself. What do you mean 'under load' and where should I check when starting?

Under load refers to testing the battery's voltage while it's actively providing power, such as during engine start. Monitoring the voltage during this process is crucial. A significant drop below 9.6 volts while starting indicates a weak battery. Given your symptoms and lack of voltage readings, it's highly probable that you have a heavily discharged or defective battery. I would advise that you take the car to a workshop as soon as possible to have it properly checked.

Okay, thanks for the detailed explanation. I took it to the shop, and it turned out that you were right: a defective battery was the problem! The repair cost was 290€. Thanks for your help!