looking to pump out my new r.o. unit into my aquarium using a standard bilge pump i will purchase at the marina . the battery weight is critical in this project. the standard pump are wired for 12 volts to work in boats i hoped to use 2 lantern batteries to run it approximately 15 minutes a month to lift the water approximately 5 feet from the floor to top of aquarium (30) gallions or so. cost is also a determining factor. pumps run 20 or so and two batteries...cheap enough for me. if it works, wire size? where can i put a switch?

 

What is the current draw and/or watt rating of the pump? If you put two 6 volt lantern batteries in series, you have 12V and roughly 15-25 Amp Hours (Alkaline/Large), so if the pump draws 5 Amps, you would get about 5 hours of use from the batteries. 5A would be a 60 Watt pump.

It may run slower, as the pump is probably rated for 13.8V, but should run at 12V ok.

Wire size is dependent on the current draw, the switch would be inserted between one battery and the pump, cut wire, insert switch. Make sure the switch is rated for over the required current as well.