How to replace a 12V battery?

You can physically replace the 12 V battery, but the ID.3 is one where I’d be cautious about doing it as a simple DIY battery swap. Volkswagen says the replacement battery needs to meet the correct specifications and that the vehicle’s electronics need to be adapted after replacement.

The battery is in the front/engine compartment. If you do disconnect it, switch the car off first and disconnect negative first, then positive. When installing the new one, reconnect positive first, then negative. The tricky part is the battery adaptation/coding afterward, which is why VW recommends having a qualified workshop do the replacement.