The charge acceptance rate varies considerable with applied voltage.  0.36 volts may mean you'll need days for the batteries to reach full charge.  Not sure if the OP has 8 ga wire on the ground path?  If so the problem is much worse.  I have 720 watts of solar and i see about the same 0.36 volts drop at > 30 amps charge rate.  And I have paralled two strands of 8 ga effectively making it 5 ga wire on both the live and ground wires.  Wish I had even larger wire.  I have seen my 40 MPPT controller max'd at at 40.0 amps after leveling and putting out all three slides.