Just get the one you have rebuilt. Its cheaper and is more reliable. Had to change one in my truck, and after my third one putting in it in 10 degree weather, i just sent it out to get rebuilt, and havent had a problem with it since. Over a grand in new alternators that didnt work Vs 80 buck to have one rebuilt with a higher output and works.
About the output, ive seen this problem and was told its not always the alternator but the battery that cant hold the charge. If the battery is over two years old and a stock one, you should upgrade to a yellow top.
Well I've been thinking of upgrading to yellowtop as well, but I have a new battery thats doing pretty good. The voltage regulator is gone on this alt, so hopefully that battery lives lol, and since its internal I've been told it can't be replaced.