I finally finished my battery backup project. I used a deep cycle marine battery, a battery box, an automatic trickle charger, a 1200watt power inverter from canadian tire(overkill, but it was half price) and a DIY transfer switch. I hacked into the inverter and wired up relay contacts in parallel to the units power switch so the inverter would turn on when the power went off.
I should be ready for the inevitable power outages this winter.
Circuit Diagram
Inside transfer switch
Rear:
Completed
The trickle charger is inside the battery box, beside the battery.