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Ohm's Law 101
To get an idea of battery life for your bait tank, read the performance data sheet for the pump you have. There should be a specification for both flow rate (GPH) and power consumption (Amps) for the product voltage (typically 12V DC). For example, I use a Whale Super Sub Bilge Pump that produces a flow rate of 550 GPH with 2.8 Amps draw at 12V DC.
So, suppose you connected this pump to a 12V 5AH battery. You should expect less than 2 hours total run time: 5AH / 2.8 Amps = appx. 1 Hour 48 minutes. Not so great for kayak fishing unless you are DORADO50!
Now, following Ohm's Law (Amps = Volts/Ohms) since resistance is constant, suppose you use a 6V 5AH battery instead. This effectively reduces the power consumption by 50%: (Amps*1/2 = Volts*1/2 / Ohms). This doubles the run time to appx. 3 Hour 34 minutes. Much better. However, since the pump now runs at lower speed, so is your flow rate going to be reduced (to around 225 GPH).
If you use instead a 6V 12AH battery for the above pump, you would expect a run time of nearly 7 hours. That is a good amount of time on the water. Again, remember that as the battery draws down, the voltage output will drop, and the pump will run even slower.
Finally, by adding an On/Off switch for the pump, you can avoid running the pump until you actually have bait in the tank (and if you run out of bait you can turn it off). That should get you through the day.
Tomorrow's lesson: Iron 101
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