2004 Volvo V70R, 200,000+ miles. I am regularly getting the red battery light. The warmer the weather, the sooner the light turns on.
Last week I installed a temporary voltage gauge to monitor my battery voltage while driving. On start-up I get 14.2 volts, it's all good. As I drive the voltage slowly drops, and below ~13.5 volts the battery light illuminates.
Eventually off throttle the alternator basically stops outputting voltage and I drop to the battery voltage, 11.9 volts. The higher I rev the engine, the higher my alternator voltage goes, but the warmer the car gets the lower my high end voltage gets, so eventually the alternator can't hit 13.5 volts and the red light is always on.
My battery is a decent AGM (4-5 years old), but the resting voltage seems a bit low, typically 12.0 volts when parked. Using an AGM charger brings it up to 12.7, but it drops down to under 12.0 after a few hours. These numbers suggest to me that my battery can't hold a charge above about 30% of the original charge level.
I
think my battery is toast, and causing the other issues, or I have two issues. It seems odd that the alternator output is all over the place (I suspect the alternator is original, so >20 years old, and >200,000 miles on it, but the voltage regulator is two years old, and came from a replacement alternator O'Reily's sold to me that did not fit). But, the car starts right up with zero signs of low current.
Normally I would replace the alternator but it is is EXTREMELY difficult to remove (rad and power steering pump are in the way, it an all day job). I can change the voltage regulator with a couple of hours of work. But, a voltage regulator from Volvo is $285! (yes, that's just the VR), an alternator is over $800!. There are lots of Ama2on 'equivalents for $50, do I do all that work for a knock off VR?
Start by swapping out the battery?
Or did my alternator take out my battery and they both need to be replaced?