Most often when we tested these alternators we found either blown diodes or worn-out brushes. These parts were available for about $20 and the repairs were extremely reliable.
But on modern automobiles when the cause of the charging system failure is traced back to the alternator it should be removed and replaced. Most late-model alternators are not rebuilt anymore. They are traded in as a core towards the purchase of a new or re-manufactured unit.
The only difference is that these internal components are now harder to find and more expensive. In some cases modern generators are put together with specialized bolts to prevent you from taking them apart.
Re-manufactured alternators or brand-new parts
One of the biggest variables is your intent with the vehicle and the current mileage on it. If the vehicle had less than 100,000 miles and you plan on keeping the vehicle for another 10 years then my recommendation would be to go ahead and buy a new alternator.
The most common length of warrantee would be about 90 days but some alternator remanufacturing companies will have a one year warranty. It is a good idea to understand the length of the warrantee when you purchase a remanufactured unit. I should also mention that more than once I have purchased a remanufactured alternator and installed it to find out that there was an internal problem and it did not charge correctly.
Although the parts suppliers have always provided me with another alternator in these situations the time and effort required to do the job over again came out of my pocket. In all of the years that I have been turning a wrench which is about 25 years, I have never purchased a brand-new alternator and had a problem with it directly after installation.
Again I'm sure that there are several exceptions to the rule and this is just my personal experience. In the end when you are replacing alternators you will have to use your best judgment as related to your own personal situation.
For more information about your vehicles starting and charging system and how it relates to the life of your battery I put together an article about car batteries on my other blog. For more of the latest posts to this online auto repair website this next link will take you from this page about replacing alternators to the blog auto repair homepage.