I am looking into getting a battery back-up for my existing sump pump (not interested in getting a secondary one put in). The only way is usually using an inverter with automatic transfer switch with battery charger. I would also be using a deep cell marine battery but it looks like to much bulk. I was told of a new battery back-up system that is compact and all encased. It also uses lithium ion batteries that will last a lifetime. Does anyone know of these or have seen them? The one I was told of was made by Xtreme but not sure. Thanks!