Loss of voltage fast and solution

[Jamescj212]

Did egr tune over the wknd and f.water sep filter as well. Truck left for georgia . Dropped from 14v to 12v over night
Had her check belts, batt connections, and shut down inverter and all else. Dropped to 10 and dies about 12 at a unloading dock. She restarted it a hour later and volt climbed back to 14ish. When she went 3 miles down street to reload and thats where a company "meeks" pulled in who said it was withou t alternator and they could get it 2mrw for about 2k. I called and found 1, they went and got. It was a band aid compared to what it needs but we cannot wait. Id like to say i found them here at oem for 1600 and will be putting it in this weekend. In the meantime, is a alternator that big even really needed? I understand the reasoning behind being thousands of mikes away under warranty, but what gives with a 1600 per unit, but why? Raining and pouring.