Help, car keeps dieing

The trouble with so called "testers" is that

1--They only show if something is bad, not good, and are only reliable if they are "honest" and the operator knows what he or she is doing

2--No typical parts store alternator tester can test an alternator under full output load. This means there is no way of knowing whether your 40, 50, 60A unit can actually output it's full rating.

In other words, these testers are fine as far as they go. They are not absolute