Emergency Power Supply Schematic Diagram

I am designing an emergency power supply.
GOALS
-The regulated source should provide power to the load when there is power in the mains.
-When a power outage occurs, a backup battery should take over.
-When the mains power is available again, the regulated source should power up the load again and charge the battery at the same time.
-When the battery is full, the charging should stop

This is my current circuit: **broken link removed**
V1: Regulated Buck supply
V2: Battery
R3: LOAD

Switch States: With Mains power, battery is charging
1) Q2 is switched on which in turn switches Q3 on. Battery starts charging.
2) Q4 is switched off since the Regulated supply voltage is greater than the battery voltage.
3) Q1 is switched off since the battery is not yet full.
4) Substate: Battery is full. Zener diode D1 lets current flow to the Gate of Q1 which switches it on.
This switches off Q2 and Q3 since the Gate voltage is insufficient.

Switch States: Without Mains power
1) Insufficient voltage switches Q2 and Q3 off.
2) Q4 switches on since the battery voltage is now greater than the Regulated supply voltage.
3) Battery supplies power to the load.

Any wrong assumptions and mistakes in my design? Any ideas? I am not yet sure if this will work.
All suggestions for improvements are welcome

Welcome, guitarnoob123!

It could be done more simply. Substitute your Buck supply (with a 10VDC unit) for the xformer/bridge supply, if you chose, for better regulation of 10VDC. Ditch the 7805 ckt.

Also, you did not state your current requirements; this ckt is obviously limited to the capacity of the 1N4007: