Ok, I'll need to check everything at home before I move forward. I think at this point all I have is a Uverse router, elk ethernet expander, and a ethernet hub that need to be plugged in to a battery backup in case someone cuts my power and then breaks in (my alarm is monitored through the internet).
So I would theoretically purchase the P212S, an extra battery, an elk transformer, plug the 212s into the transformer, the 212s into the battery, cut the end of the wires for the three devices currently plugged into a wall socket and splice them into the p212s? The Elk is on it's own battery, then these three will be on a battery backup, so if the power is cut, I should have the elk, ethernet expander, internet, and all other ethernet devices in working order for a short period of time. The only thing I need to check is the voltage on the three devices currently plugged into the socket, they need to be 12v?