Auris hybrid weak battery

Flickering lights and a weak start definitely point to a battery issue. A healthy battery should be around 12.6 volts. Have you checked the battery voltage when the car is off? If it's significantly lower, it could be a sign of a failing battery or a parasitic draw. It could also be the battery sensor, which tells the car how much to charge the battery. If this is bad, it can cause all sorts of issues.

Okay, so how would I check the battery sensor, and what should the reading be? Is that something I can do myself, or is it better left to the pros? What kind of damage am I looking at if it is the battery sensor?

Checking the sensor itself usually involves a multimeter and knowing what the resistance values should be, which varies by sensor type. Based on the symptoms you described, and the behavior of the car, I'd say take it to a workshop. A defective battery sensor can definitely cause these symptoms and could damage your hybrid system. You don't want to mess with that.

Thanks for the advice! I took it to my local garage, and you were spot on. The battery sensor was indeed defective. They replaced it, and the total bill came to 315€. Now she's starting like a dream, and no more flickering lights!