Help wiring backup battery

[Flyyak]

my main electrical buss is a 20 slot cooper bussman fuse block with 10 slots for main an 10 slots for avionics. I have a glass panel with G3X, GNS 430, Narco Mk12D w/GS, 240 audio panel an 305 autopilot.

I need help with a simple wiring diagram to add a backup battery. I plan to use a stand alone LiFePo4 continuos discharge battery and did not plan to attach this to my alternator for charging. I have a PC680 as primary battery for starts and I have an aux piper plug in the event I need a jump.

I hope to be able to add all but the Narco as essential items, add to circuit by using a backup battery switch with diode so that current flows only to avionics buss but prevents charging from alternator or primary battery. I have read that the danger to about the LiFePo4 is greatly reduced and occurs mainly as a result of charging/ over charging/ or imbalanced charging.

I am not an electrical guru, so any help would be appreciated.