The power is all cut off.
whatever circuits are desired to keep can be easily identified.
The others, simply trace back the color of your choice.
Place the battery, not at the box, but at the outlet, switch, junction box of choice and one can locate all the outlets, switches, etc on that circuit.
I've done it several times using even a ohm meter. And a long length of wire.
While you're at it is also possible to check leakage to emt.
fwiw, pulling in new wire and cleaning up any past fubars may be a good option for op.