Alternator Issue?

Tell me what you think about this issue:
I flew 4443H ('79 Mooney 201) Saturday morning for a couple of hours.
One time during the flight, for about 5 minutes the High / Low voltage
light was flickering. It did stop flickering, the ammeter wasn't showing
a discharge, and the battery voltage remained above 13 volts so I didn't
worry about it. My partner then took it for a couple hour flight. At his
destination he forgot to turn the master off so when he returned he
needed to get a jump. He got it started, took off, was flying home, and
after 30 minutes or so lost all electrical power. He made it home and
after a manual gear extension landed without incident.

Alernator History:
The alternator was rebuilt 800 hours ago (2001)
I am unsure about the voltage regulator
New battery (GIL 35) 7 months ago

Is it possible that the battery just needs to be charged (low on water
maybe? I know probably not) or does it sound like the alternator /
voltage regulator has headed south? Maybe a set of alternator brushes
would cure the issue?

If we need to get a rebuild done can I get some recommendations for
shops (prices?) Also do you usually replace the voltage regulator at
this time too?

Any info or experiences would be appreciated. Thanks!!

Jon Kraus
PP-ASEL-IA