Problems which look like alternator failure?

[FireFox31]

Are there other problems which might look like the symptoms of a bad alternator? I want to be sure the alternator is the problem before wrestling to remove it and installing an expensive replacement. Thanks.

On a 1998 V70 T5M with 178k miles, my symptoms are:
Car electrical systems fade and die after 22 miles of driving because battery got totally drained; started full.
Using a multimeter, a charged battery reads 12.6 V with the car off, 11.87 V with the car at idle with accessories off, and 11.80 V at idle with the fan on full and radio on.

I spoke to the previous owner of the car and he was surprised to hear that the alternator had died. He had the car sitting for the past six years and had a tender on the battery. He said it came to a point where the tended battery wouldn't start the car. This makes me think he ran the car occasionally during those six years on a dying battery. Could running on a failing battery harm the alternator?

[misha]

It's alternator or voltage regulator...but first...use digital multimeter and measure alternator output directly on it.
(+)probe on b+ terminal and (-) probe on alternator housing.
Healthy charging system should read 13.8-14.2v at idle with headlights,radio and heater blower up to 2nd speed.

Driving a car with low or bad battery will cause an alternator to overheat and cook the voltage regulator.

I'm surprised that you don't have a battery light on.
Do you?

[abscate]

That’s a dead alternator, alright. Even at idle, that voltage should we well up over 13 Volts

Have a good look at all the positive and negative cables though, and look for voltage drops with the lights and brights on