6 gpm DC pump for 24-hr operation

Hello- I looked for other threads with this discussed but didn't find one that I could use. I have a local farmer who wanted to run his 6 GPM water pump 24/7 through the winter months. He does this for cattle troughs to keep the water from freezing. He currently uses batteries charged at home and delivers a new battery each day. The pumps he uses now are around 14A and the batteries/panels for that amount of power is more than he wants to pay for.
Are there any lower amp pumps available that are in DC that would allow him to skip an inverter and run straight from the batteries/panels at less than 14A? I see some Flojet pumps, etc., but I am not familiar enough with the specific types of pumps (diaphragm, centrifugal, etc.) to know what types would be good.
I did tell him to try use other methods such as heaters or passive designs, but he knows his current method works and he wants to keep using batteries. I just thought it was an interesting problem to help him with.
Comments
Most important in calculating the power draw (and type of pump) is knowing the pressure that the pump must produce in order to get 6 GMP flow.
If you are using the pump to pressurize a 60 psi air bladder tank, 6 GPM will take a lot of energy. On the other hand, if you are using a low pressure circulator pump to keep water moving in a stock tank, then that same 6 GPM will take much less energy.
--vtMaps
The current pump is exposed and does not freeze, and it may just be in a small unheated box. The pressure (psi) will be close to 0 as it is only pumping into an open-toped water trough. I think your "low pressure circulator pump to keep water moving" is the accurate description. I see some pumps like the http://www.pumpvendor.com/Jabsco_82600-0294.html that move 6 GPM at less than 2Amps when pressure is near 0. I'm not sure how realistic this is though...sounds too good to be true?
Circulator pumps are similar.... they can't tolerate too much resistance (filters, valves, thin pipes, etc).
As your pipes begin to freeze (from the outside) the water current is constricted to a smaller diameter and the circulator pump may not be able to keep the pipe from freezing through.
The big pump makes more pressure, and can force the water through a thinner channel. The friction of the water against the pipe actually warms up the water.
What sort of low temperatures is this watering system exposed to?
--vtMaps
It's so hard to know how much trust I can put into their pump curves. The one he uses has max 17Amp but pump curve at 0 psi would be around 7-8Amps. Huge difference when trying to design the proper system/bank.