I have a 2015 Yamaha with new batteries. On a level street, I can get about 30-minutes of run-time, and then it begins to slow (or die). I installed a meter, where I see 50V and 170AH after charge. In addition, each battery reads approximately 8.5V with a multimeter. It seems to get a proper charge, but does not sustain life. What am I missing? What can deplete batteries quickly? Is this a grounding problem, a motor/cable problem or other? Thanks in advance.