In preparation for finishing our basement, we want a back-up sump pump and a radon mitigation system. One aspect of the radon system is having the sump specially sealed. My plumber is familiar with water-powered pumps, but says they're not compatible with a sealed sump (something must be able to move instead of being held in place through the sump cover). Hopefully a battery-powered backup will not have this limitation. Does anyone know if/how a battery-powered back-up sump pump will work in a sealed sump?