S60 Hybrid Additional Battery Alarm

Sounds familiar. I had a similar issue with my BMW 3 series, also hybrid. Battery check is the first thing I would do.

Could you tell me more about the issue you had with your BMW? Were the symptoms the same? Did you check the battery yourself, or did a professional do it?

Sure thing. My BMW had the same battery signal issue and the alarm went nuts. Couldn't figure it out myself so I took it to the workshop. They confirmed it and replaced the battery.

Thanks for sharing your experience. I took it to a Volvo workshop, and they said the additional battery was discharged due to age. I've approved the replacement, which will cost about 330€.