So, I have a 1991 Mercury Capri. Recently - on Halloween, no less, spooooooky - I drove to work, and like a dumbass, left my lights on. When I came back out, my battery was ofcourse dead. I got a jump from a helpful stranger, but after a few moments, the car died. Another jump, another car death - it appeared that either my battery was simply not holding a charge properly, or the alternator was dead. Most would say that it would have to be the alternator, since most battery problems like that aren’t that sudden - this happened all at once, and I hadn’t had nary a problem before this.
Here’s the interesting part - since the first step in diagnosing alternator problems is to make sure it isn’t something else, I went and had my battery tested. It was ofcourse dead, so they had to charge it at the AutoZone where I took it. When the guy put the battery on their charger, the charger accepted it, and it tested good to be charged. However, once it had gotten to full charge, it tested it again at the end of the charge cycle, and it tested bad. The voltage was between 13 and 14 volts, which should have been just fine, but it apparently failed on amperage. However, their machines (and the machines at a few other auto places I visited) won’t show the specific amperage the battery is putting out, just a pass or fail. I have no way of determining if the amperage is just barely falling short, or if it is really failing.
So, my issue then, is that I think that the battery is good-e-nuff to chug on for a while, and thus I need to go ahead and replace my alternator, but I have no way of being sure. The symptoms match a dead alternator, but there is enough evidence of a bad battery that I’m not comfortable going ahead and acting on the supposedly dead alternator. Does anyone have a way I can rule the battery out as the culprit here? I only have the funds to replace one or the other, not both.