No Charging Problem troubleshooting options at a loss now

Depending on how "Bad" the Battery was ...  The Generator can only produce about 5 amps at idle speed.

If the battery and the panel circuits are trying to draw more than that, the voltage will sag until the the load become less than the capacity.

Did you observe if the voltage improved with RPM?

Bill,

When we were flying the battery and all voltage went so low we lost all comm, instruments, everything dead (besides the engine running which I care about the most). When we got back and landed the voltage it the battery was 1 or so volts. In our troubleshooting, we would have 12.3 or so voltage measured at the battery after charging it externally, start it up, the voltage would not change at all and as we would start to load it (start to turn on lights etc) the voltage would slowly start decreasing. Looked as though the battery was fine and just now charging. We would run it up to 3500 rpm and no effect. In my ultimate wisdom from that procedure, it clearly was not charging and the battery was fine (not the case). All this troubleshooting and finally the battery change out fixed the problem.

So long story short, yes we did run it up to 3500 RPM and no change to the voltage from idle.