Originally Posted by Phalcon51

Sure, you can do it yourself if you can get your hands on a 0-20v DC digital voltmeter.

Set the selector dial to the 20 volts DC scale and attach the red lead of the voltmeter to the positive (+) side of the battery and the black lead to the negative (-) side. A fully charged battery should read approx. 13.2 volts DC. Have a helper start the engine and raise the idle to about 1500 - 2500rpm. The voltage should climb to 13.5 - 14.5 volts. Check again with the headlights on, should be about the same, maybe a little lower. If the reading is 13.0 volts or less then the charging system is not doing it's job. Since they replaced your used alternator with another used alternator it's difficult to tell if the problem lies with the alternator or the regulator without bench testing it, although I would agree that it's most likely the regulator that's at fault. And you still don't know the condition or age of your battery. A battery will generally last between 3 and 6 years, and doesn't usually give a lot of warning before it dies. You might consider doing the basic voltage tests yourself, post your findings here and then take it to the shop and have the battery charged and then load tested and the alternator/regulator tested for charging output level.

The voltage regulator sells for between $24 and $34 from FastLane and is pictured below. It's very easily removed from the alternator to check the brush length or replace the unit. You can see the regulator mounted on the back of the alternator at the 6 o'clock position in the 2nd picture below.

Hope this helps

Gary