2006 Prerunner Voltage issue

I have seen batteries drain. not charging and fully charged batters sounding very weak, barely starting the vehicle. Both problems fixed by cleaning the battery terminals which visually look clean.

Having the same issue after changing the alternator doesn't completely rule out a bad alternator. It seems more likely the issue is somewhere else rather than two bad alternators. But it can happen.

Try cleaning the battery terminals and the connectors on the cables connected to the battery.

 

UPDATE, last week I had a replacement alternator put on. Fixed the issue and now I'm consistently pushing 14-13.6vdc. Initially I charged the battery to 12.8vdc and was doing fine, but not pushing the 14-13vdc. I returned the New/take off and they checked it and it was indeed bad. I'm going to submit the work invoices from the mechanic and see about getting reimbursed for the install on the second one. My voltage now stays at 12.8-12.5vdc on the battery.

And for those that say the USB reading is not accurate. I would agree with that generally speaking, but on my sample, it's been dead on. YMMV