I had a similar issue with my 2012 XC70. I purchased a battery at Costco and when the low battery light came on I went to Volvo and they said the charging system was ok and the battery must be bad. They said sometimes batteries sit before they are sold. I doubt that would happen at Costco but I went back and got another battery. The light came on again and then Volvo said when you put in a new battery the system needs to be reset. They changed $50. No issue since.