If you want to see how long those batteries will last at 30-watts power draw, use Ohm's law again. The formula for this is I=P/E. This translates 30-watts at 12 volts draws 2.5 amperes. Now, that AA battery is rated at 400 mAH. So, 8 batteries equals approximately 3200 mAH, divided by .410 mA. At best, you'll get approximately 8 hours operating time before the batteries are completely discharged to "0" voltage. Of course, the system will not operate on a voltage much lower than 10-VDC, which would take less than an hour to reach at 410 mA power consumption.

Learn anything yet?

Gary