One of the most frequently asked questions about electric vehicles concerns the usefulness of a 12 Volt battery in a car that already has a large 400 Volt main battery. The answer boils down to two key reasons: safety and cost. Traditional 12 Volt batteries use proven lead acid technology, making them much more economical than the newer 12 Volt Lithium batteries that are increasingly common in high end electric vehicles. Furthermore, many on board components, such as lighting, comfort systems, infotainment, and other devices, operate more efficiently at 12V. Running them directly from the high-voltage battery would require a continuous voltage conversion system from 400V to 12 V, complicating the system and increasing costs. In terms of safety, the 12 V battery acts as a backup system: it allows emergency devices, safety systems, and infotainment to remain active even in the event of a main battery failure or low range, thus ensuring an additional level of safety and functionality while driving. Not only that, the low voltage 12 V battery is responsible for managing the high voltage battery. Typically, the 12 V battery needs to be replaced every 4-5 years, as required by many maintenance schedules. Now, problems with the 12 V battery can also cause charging issues. The reason is intuitive: the 12 V battery powers the infotainment system, including the charging system. Before blaming the 12 V battery for charging problems, it's advisable to isolate the charging issues and perform a separate diagnosis. Statistically, when a 12 V battery is replaced, it's less likely to be responsible for BMW i3 charging problems. However, it is always advisable to have the 12 V battery replaced by experts in the sector, by an auto electrician or by BMW Service, as they also carry out any updates and settings that prevent the emergence of future problems.