I used roller pumps for a little while for spraying roofs,. they do spray really well, but they don't spay with the same oomph after a few weeks of work. And that was with rinsing. To me they have to be rinsed or they will be trash in a very short time. Bottom line is they do work, and I love the way they spray when they're new, but that downfall of the pump is irritating. Just keeps losing velocity and you start having to try and compensate by sneaking the engine RPM's up. Then the pump dies. I now use an air diaphragm pump and used it all last year, and it still works the same. But using a roller pump to start with would be fine, better than messing around with the 12v electric in my opinion.
Jeff