Amps absolutely, and here is why.
Eventually, the battery will start to fail. Often, it will fail by shorting out one cell out of the 6. That means it is now a nominal 10 volt battery instead of a nominal 12 volt battery, BUT the fully charged voltage might be 11.8 or 11.9 so you will not notice it on the voltmeter.
When the battery cell fails, the alternator is going to try REAL hard to charge the battery, and it is going to be doing it ALL the time. The end result, as I have found out in 3 (footnote 1) cars, is that the stator winding in the alternator will overheat, the insulation on it will break down, and it will short. You will then need to get a new stator winding from wai-wetherill and rebuild the alternator.
http://www.wai-wetherill.com/products/ymm.cfm
(They dont have the parts for a yaris alternator yet, too new, but they have all the little itty bitty internal parts for all the older toyota alternators and starters. I look up my part number and then phone my order in to the distributor in Boston Massachusetts :
Boston Auto Electric
103 Clayton St.
Boston, MA 02122
Toll Free: 1-800-225-6650)
Put the ampmeter into the alternator output wire so you will know about this event BEFORE it becomes fatal problem.
(footnote 1: Experience is the second time you make the same mistake. I have no excuse for the third event.
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