The pump listed can run dry without damage. With very low voltage it just doesn't pump much or at all. A submerged pump won't warm up much anyway, as the water around it carries the heat away. You can test this yourself if you have a battery powered weed whacker. Put a few volts on it and it will just sit there. Bump up the voltage a bit and it will spin slowly. Only when you get to a certain voltage/current combo can you do useful work with it. As long as you don't lock the rotor you will have no trouble. You need to clean the intake screen at regular intervals, too, otherwise it will not pump.