[Blazer Rattle]

I was stopped at stop light - went to take off and was moving when all of a sudden my blazer died - now lights would start or go into gear - I had it towed to dealership and they’re telling me it’s battery - I find it hard to believe while moving the battery would just kill the car while moving - also prior to this had the power steering assist message come up - anyone else experience either and what did dealer do ? Thanks in advance for help