Hi CW,

Both our 960 & S90 only hit about 14.7V immediately after starting and then then within a few minutes are down to about 13.8V. Both consistently perform the same way.

18 Volts is scary. Is the fluid in your battery foaming or bubbling? Batteries can explode when subjected to overcharging.

I would suggest checking your static battery voltage after the vehicle has been shut off for at least 8 hours. This can give you an indication of the state of your battery. It should be ~12.7V

I am not an electrical expert by any means but find it interesting that both your cars charge in the 16V range and both of mine charge in the 13-14V range.

The VR is of a diode design and is integrated into the alternator. Others on this list have replaced the diodes to correct similar problems.

I am wondering if you have a corroded connection or fault in the battery causing the VR to put out more voltage to compensate. Perhaps you have a very high draw only when the engine is running. Most likely it's the VR but on both cars??? Again, I am no expert.

Other will add that have more experience.

DEWFPO
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1998 S90 077,400 and 1995 964 154,100