Hmmm .... my 12 volt true deep cycle AGM batteries so far seem to follow this curve pretty close .... and the little EX650 will power it doing this, too, for up to about 5 hours on 1/2 gallon of fuel. I wonder where the tester found a Group 27 deep cycle battery (wet - not dry - cell, I assume):
http://www.parallaxpower.com/assets/site/docs/PPSCONVERTER/7300_7400%20Series%20Battery%20Charge%20Curve.pdfBy the way I would concede - and go to a double voltage with timed high-voltage stage - charger ... if Parallax still made the 7455T converter. Does anyone know where I can find a good used one?(scroll down to the 2nd page):
http://www.parallaxpower.com/assets/site/docs/PPSCONVERTER/7400%20Series%20Brochure.pdf