It might be worth trying to adjust the camera settings through the web interface when you’re that deep - increasing the brightness and contrast, and possibly gamma as well.
Choose whatever makes the most sense for your application. If you don’t need control of them then 5 is fine. If the always-on light is problematic in the less deep portions of the dive then having dimming control may be a requirement. 
The technical details I linked to in my previous comment specify that the peak current of one light is 15 / V_in amps. Since power is current x voltage, you can assume the peak power usage is 15W. I’m not certain if the peak power usage is consistently used when full brightness is applied, so the average power might be less than that, but that at least gives you an upper bound. You can also measure the voltage and the current usage with a multimeter or oscilloscope if need be, to get a more accurate estimate of expected power usage of time.
There doesn’t seem to be a guide on doing this at the moment, but it’s not too complicated - you basically just remove the four screws and then carefully pull out the end cap (as discussed here), and then you can unscrew the blank penetrator nut and remove the penetrator.
It’s possible a guide could be made of the process if you’re interested, but it could take a few weeks to a couple of months, which may not be soon enough for you to make use of it.