Highplotter, sorry to join the discussion so late, but thought I would add my 2-cents worth. I design battery plants for telephone offices and have some thoughts.
I assume your 130-volt dc batteries consist of of 60 cells, correct?
With the rectifiers on, the batteries should float at 135 VDC (2.25 volts per cell). Once the rectifiers turn off, for what ever reason, the batteries would supply power. Intially when the rectifiers turn or trip off-line the voltage will drop from 135 to about 125-to-130 VDC, then slowly discharge to a final discharge voltage of 105 VDC before exhausted.
A dip of 50 volts as soon as the rectifiers trip off-line indicates a serious problem. It could be a lot of things like:
Shorted cells
Open cells.
Bad batteries in the string
Poor terminal connections.
If I were you, I would get my hands on a DLRO ASAP and test all the intercell connections, battery terminal connection, and battery conductance.
