The numbers aren't too impressive. Here are the figures, from the electrical chapter of the Haynes service manual. I'm not sure of the accuracy of these numbers. The third problem is one that is not inherent in the design of the system. It comes with time, age, and corrosion.
Maintenance is rather simple, but tedious.
Just keep all connections clean and tight and make sure to inspect the alternator brushes regularly. Heaven knows Bosch uses this basic charging system on every alternator-equipped VW I've ever worked on, so the odds seem good that they'll use it at every opportunity. Here's where we get to the part about how the charging system actually works, but first a note about the schematic provided. This schematic is highly simplified to make it easy to follow. Connections which can become corroded and cause trouble.