If you are sure about the battery then the next place to start is the charging system. You indicated that the charging system indicated a discharge issue, and you landed and made a second flight with the same condition.
The engines started fine for the second flight? No battery issue after having the discharge indication?
--Yes, Battery was fresh after my initial landing and subsequent VFR flight home only because I shed enough load and only ran one radio. The system would charge around 24.9v but the second I put the taxi or landing lights or any other accessory, the system charging voltage would drop below 24v. After a 2hr flight at 24.9v on one radio, the battery would be topped off again.
--For years prior, I could get 26-27v no problem with either regulator selected. There would be about a .2-.3 difference between the two. Now both regulators are acting the same in a discharged or "weakened" state which from a trouble shooting stand point would kind of eliminate, at least for now, the regulators I would think. What are the chances of them both going out at the same time and acting the same? Now it is as if the system was weakened somehow but still working only at higher rpm's. On the ground just a full discharge. Again, while on the ground if I switched the Alt's off, the amount of discharge would lessen. Turning them on at low RPM caused a higher discharge.
During discharge situation, could you determine if it was both front and rear or did you try to isolate it besides the regulator select? Did you try switching off the alternators one at a time?
--I did and my findings seemed to indicate that both ALT's were acting the same. On the 68 system, do both ALT's get Regulator voltage from one Regulator at a time?
--This is truly strange and may be a diode or wiring issue since I do get charging (a greatly diminished charging voltage only at higher rpm). If the Alt's were shot, would they put out at all? Would worn out brushes cause that or do these Alt's even have the spring style brushes inside like other Alt's?
Here are some threads that may reveal some insight. Just be careful that the system is the same as yours as Cessna did some changes throughout the years. Your '68 is different than the newer G models
http://www.337skymaster.com/messages...ight=discharge
http://www.337skymaster.com/messages...ight=discharge
__________________
Herb R Harney
1968 337C
I'm in the front of the aircraft to prevent it from committing suicide