Operating Voltage and Current of solar PV panel connected directly to a battery
Given that 12V is largely lower than your Vmpp, your PV panel will operate in the constant current part of the characteristic. The current will be close to Isc. Is it then easy to calculate the voltage.

EDIT: I forgot I have a simulation of a PV panel here that could help explain what happens when you connect the panel to a rather low voltage battery. The characteristics are not the same as in your example, but you can simulate the same kind of operating points. Click on the switch to select the battery, and choose an emf (fém in the web page) below 12V. You will notice that the current stay close to Iscc (5.3A for 1000 W/m2 and 25°C).