I recently had some of the same symptoms with my 2015 Audi A4 Quattro. I had to crawl through to open the boot as well. Once I had it open I pulled out my spare tire to check the battery underneath. It ended up being the 110-amp HSB strip fuse that needed to be replaced. Located on the positive terminal of the battery. This is a high-current, bolt-down fuse that protects major electrical systems (main power distribution/charging circuits). It’s not a regular blade fuse.
I was told it typically protects power distribution circuits such as the alternator charging system, engine-bay fuse panel, and other high-draw modules (ABS/ESC, electric steering, cooling fans, etc., depending on trim/VIN). If there’s a short or overload, this fuse blows to prevent wiring damage or electrical fires.
It’s usually located near the battery or engine-bay fuse block, not inside the cabin. When it fails, symptoms can include no-start, loss of charging, multiple warning lights, or sudden electrical shutdown.
OEM Littelfuse matters here—correct amperage and design are critical. Always disconnect the battery before replacing and never substitute a higher-amp fuse.
Once I replaced that fuse, the issues were resolved. Definitely worth checking if you’re seeing multiple electrical problems or power loss at the same time. I plan to get diagnostics done next week, the fuse did its job but I want to know what caused it.