Installation of twin brushless motors

I have recently installed twin Turnigy AquaStar 4084-620KV Water Cooled Brushless Motor coupled to two Turnigy Marine ESC 120A.. I have wired the two ESC's in parallel with a 12v sealed lead acid rechargeable battery. (7ah). I have set up the throttle range as per the instruction, and the motors are wired to run counter clockwise to each other. When I run the motor, at whatever throttle position the motors run for around 20 - 30 seconds then stop. Bringing the throttle trigger back to neutral and trying again the same thing happens. If I turn the power off to the ESC's and switch off the transmitter, switching on and going through the normal working mode start up, the motors do not work. I'm using a pistol type transmitter and the motors are installed in 1.5 metre long boat. This issue is without the boat being in water, just spinning the props dry. This is the first time I have used brushless motors and so have limited experience of setting up the ESC's i'm just working from the very limited instructions in the two page booklet that came with the ESC's. Thanks any help or suggestions would be gratefully received.