On the first replaced alternator (which turned out to be bad), it only happened once, and the battery was dead and were not able to start back up -- this alternator tested bad so it was replaced a second time.
During a test drive today after mechanic checked battery, alternator, and all circuits and wiring for amperage and all were good, and OBD showed no fault codes, he said it died on him. Initial attempts to start failed, so he waited 5 minutes, and then it cranked right up, and the battery was not drained, which makes sense since the second alternator is still testing good.
Said he looked for "freeze frame" codes on the OBD afterward and nothing showed. His theory is that some component is randomly sending a code to the PCM which shuts it down.
As to per day, since the alternator was replaced a second time approx 2 weeks ago, only happened once to my son on Tuesday, after which I recharged the battery to make sure I could drive it to mechanic, and checked for amp draw with ignition off to see it something was drawing current overnight (no draw). The next time was what I described above, to the mechanic on test drive after they could not find anything testing bad. Said something like "we're at the point where we would have to start pulling panels off and charging you" since all fuse box and wiring tests came up with nothing.