Intermittment Voltage drops and Touch Screen Freezes

[SkiBum2002]

2013 VLX with 350 hp

What could be causing voltage to intermittently drop to 12.3-12.5v (normally runs 13.6-14.2v) while engine is running?   Voltage drops seem to be onset by engine loads (surfing, pulling wakeboarder with ballast, etc.).   This weekend we had a few long surf sessions followed by a slow ride back due to rough water.   Voltage got below 11.5v triggering warning lights/sounds.  Not running stereo or lights but did use blower around engine starts and ballast pumps when setting up surf and wakeboard sessions.  Oh and the touch screen freezes but I take that is related to the voltage drops.

Running two 750 CCA Super Start AGM connected via a On/Off/Combined switch an BEP voltage sensing relay.  Both batteries are cranking batteries - didn't have a Deep Cycle battery when i replaced them in June.   

I notice when i put the charger on one battery, initially the charger reads 13.9 - 14.1v but after several minutes of charging (2A mode), it reads 60-70% charged.   Is this caused by the VSR kicking in?

Thanks for the help.

Mark