Basic questions: How old is the battery? 5 years is about as much as you can ask for. Are the terminals clean and free of that white powdery corrosion? Baking soda and water mixed to an oatmeal consistency will clean that crap right off.
Belts: how old?, Shinny where they ride the pully, cracked, loose? Belts are good for 60,000 or 5 years.
Voltage regulator: Start the car with all accesories off, read the voltage. Start turning high-drain things on like the blower, lights on hi-beam, cigar lighter, rear window refogger. If you notice a drop for each additional load your regulator is not keeping up and you are running off just the battery.
Your alternator can produce as much as 16.5 volts at max output. With all the voltage drops along the way, you might see only 14.5V at the fuse box where your dash meter is looking. I found voltage regulators to be suspect after 150,000 or ten years. Check all your fat wires under the hood, Volvo's Achiles's heel has always been the wiring, chech your fuse box for corrosion, that may explain the rough running. Any white powdery corrosion on the fuses is bad, I just get new one's, they are cheap enough.

Steve M.