C70 weak battery flickering lights

I had something similar happen with my C70. Does the battery light come on at all? In my case, it turned out to be the battery sensor. It's responsible for measuring the battery charge and telling the car how much to charge it. When they fail, the car often undercharges the battery. Have you checked that?

Battery light hasn't come on, no. Battery sensor, eh? Whereabouts is that located, and how would I go about testing it? Is it something simple like a fuse, or am I looking at needing special diagnostic gear?

It's usually connected directly to the battery, or very close to it. I wouldn't mess with it too much yourself if you're not sure, as you could damage something, or worse, hurt yourself. From what you describe, it does sound very similar to what I experienced. I'd suggest taking it to a workshop, they can run a proper diagnostic and confirm if it's the sensor.

Thanks for the tip! Took it to the shop, and you were spot on – faulty battery sensor. Cost me 315€ to get it sorted, including labor. New sensor fitted, and the weak starts and flickering lights are gone. Appreciate the help!