1998 Accord, auto tran, 4 cyl. (daughter's car)

The brake, door, and battery light came on while driving. I checked the voltage ( batt = 11 volts not running, but when running, the volts was going up and down between 14- 16.3 volts).
So, I figured the voltage regulator in the alternator was funky.

When I started to disconnect the battery, I noticed one of the connectors was loose. So I tightened them up, and the light went out.
She drove around for 5 days, then the car quit on her. Pulled the car home to check things out.

The battery was 9 volts, so I assumed the alternator gave out. While I was taking the alternator out, I was charging up the battery, but the charger volt needle was jumping up and down between 9 and 13.
So I took the battery and the alternator to the auto store and they said both alt and the battery was bad!

Good thing I have life time warranty, and got free replacements, but how the heck do BOTH go bad at the same time?
1) Was the battery starting to go bad and cause the alternator over work and go out?
2) Or was the alternator going bad and damaged the battery?
3) or did that loose battery connection start the trouble?

 

There is no way to definitively tell what failed first. Depending on the age of the battery a few dead cells could have overworked the alternator.

 

Also possible the loose battery cable caused the voltage regulator to go all over the place chasing its control point - the voltage spikes causing the first actual damage to the regulator. It would be very difficult to prove which thing happened first.

 

OK... I am the kind of guy that likes to understand what happened and why...