Battery or Alternator?
 

2001 Volvo S80 2.9 Non Turbo

For about six months now a message would pop on the dash "low battery voltage". It'd stay on for about a minute then go off. No big deal. It'd happen once out of every fifteen trips.

This weekend I took it to MA. About 20m from my house battery message came up. About 2m later a red light with a picture of a battery kicked on. Then ABS lights. Then I lost the speedo. Then it started downshifting. I lost my lights and I pulled over. I got it towed and now its at my parent's house in MA.

My Dad charged the battery and it started fine. It was idling for a bit no problems. Still said low battery voltage. He pulled it out of the driveway and everything died on him. We're pretty certain its the original battery and alternator. So does it sound like the battery is junk? Or is the alternator not keepng the battery charged? Can an alternator only work at 50% capacity and simply the car is using more power than the alternator is recharging at?

There is a voltage regulator in an alternator and a failed regulator (or even alternator) can cause all sorts of voltage issues in the car from too much to too little.

I'd get the battery and alternator tested at a local auto parts store (ie. Autozone). Just take both out and bring them to the part store and ask for them to test them. Honestly, it sounds like the alternator is shot.

Someone else mentioned that too. So the regulator is in alternator?

How big of a job is this? I am doing this on my own. Though, my expertise is lifted Jeeps and Samurais; little less wiring in a 50 horse carbureated 1300cc engine than my Volvo's, haha.

The alternator is pretty easy to remove, you just need to remove the accesory belt, connector and a few bolts. The voltage regulator is a seperate part, but most likely you'll need to just replace your whole alternator.