Seat Alhambra Undervoltage Issues

Sounds like a classic undervoltage issue. Have you checked the battery voltage with a multimeter while the engine is off? Should be around 12.6V. Also, check for voltage drop when you try to start the engine. If it dips below 10V, the battery is likely the culprit. Could also be corroded battery terminals causing a bad connection, so inspect those as well. Battery health is key for modern cars with lots of electronics.

What do you mean by voltage drop? How do I measure it and what am I looking for?

Voltage drop is how much the voltage decreases when you put a load on the battery, like when starting the engine. A healthy battery will maintain a good voltage even under load. If it drops too low, it indicates the battery can't deliver enough current. Given all the symptoms you're describing, and considering the age of the vehicle, a defective battery is very probable. It's probably best to have a workshop confirm the battery health.

Took my Alhambra to a local garage, and you were spot on. The battery was heavily discharged and failing. They replaced it, cleaned up the battery terminals, and everything seems good now. Cost me 290€. Thanks for pointing me in the right direction!