Lights on power off

I'm not sure this is doing exactly what you want as the mosfet is always on and if you measure the current of the dc supply it's just reduced slightly when the ac voltage is on (and will drain a battery). It would be much better to do it with relays so you can fully isolate the two supplies, but if you wanted to do it with a mosfet have a look at https://everycircuit.com/circuit/4911188871479296

Hey thanks for the advise. It was mostly just an idea I wanted to try out. I appreciate your tip and circuit. I really thought the mosfet was the way to go too. Can't win then all right?

No problem a Mosfet should work fine, would be smaller and could be needed if you have something hooked up that's sensitive to drops in the input voltage. But they can also fail and stick on where as if a relay fails it will only ever be in one position or the other so you shouldn't be able to use both supplies at once. My personal preference for a relay would also be that they can be powered of the AC supply directly so you're battery is effectivly disconnected when you have power and there is no drain from the control circuit without any other components. But both are valid options it's mostly my opinion that relays are better.

I wouldn't go down this path unless it's completely isolated and fused, I personally would find any working power supply up to 15v to act as the power out indicator and tap off some of that to float the battery until the time comes it kicks in power

Fused yes, isolated no point.