Charging issues with Toyota style Denso Alternator

What electric fan?

The battery either checks good or it doesn’t. The whole “near the end of its life” thing sounds like a salesperson trying to sell you a battery. It could be lower voltage than it should be, but that could just as easily indicate a charging problem. If the voltage is low you have to rule out a charging issue. Or buy a battery and cross your fingers, because if it’s a charging problem that won’t fix it.

Also consider the fan motor could be on its way out, overheating and drawing too much power.

I run my ford contour dual electric fans with a 100 amp Tuff Stuff alternator, not even a Denso which should have a higher output in lower rpms. I can understand the 60 amp possibly not being enough at idle especially when the fans first kick on, mine draw between 30 and 40 amps at start depending on who you ask. But 80 amps at 833 rpm should be more than enough.

The underdrive pulleys could definitely be an issue. Just because the alternator pulley is standard doesn’t mean much, it’s all about the ratio between the crank pulley and the alternator pulley. If that ratio isn’t stock or close to it, that could be the issue as the alternator will be spinning slower and you’d get a lower than rated output.