Originally Posted by pigjamelectric
I noticed my 2004 Dodge truck has been showing overcharging on the voltmeter for a few weeks since I replaced its dead battery. (The dead can't hold a charge for more than a day. I wonder if it's this overcharging that killed it. Anyways...)
I just checked the voltage of the new battery with a multimeter. 12.5 V when turned the engine is off and just over 15 V when running. I heard this may mean a problem with the alternator. I assume the regular would be responsible for allowing the overcharging? If so, is it worth replacing the entire alternator, or is it common to replace the defective part within?
15 volts is higher than typical but not so high that the battery will go up in smoke. Keep an eye on the battery, if you can check the cells look to see if the electrolyte remains above the plates once a week or so. Sometimes a new battery will soak up quite a bit of charge especially if driven short periods between starts. You might want to put a load test on the new battery to see what its state of charge is, new doesn't mean good, especially if it's one of those from a big box parts stores regardless of the version you bought.
Yes a dying regulator or alternator can take out a battery and conversely a dying battery can take either or both of them out. There is a lot of interdependency of parts within charging systems.
It's been suggested you check the grounds between engine and battery always a good idea, they get corroded increasing the resistance thru the connection, the regulator will raise the power output of the alternator to overcome this if it has to burn it to the ground doing so. Same can be said for battery cables. The battery connections need to be clean. The same can be said for the crimp ends on the cables, the wire and the terminal corrode inside that junction increasing the resistance across the joint to which the regulator will redouble the alternator's efforts to bridge power across that joint if it's dirty.