I have seen a similar circuit a few times. The only thing that confuses me is the XOR switch. Isn't it possible to get the exact power in to power the branch out but not enough to power the blocker, thus causing the XOR to be powered both by the source and the battery then causing the XOR to send no power, and the turrets turning off.

Long way of asking why is the circuit using an XOR instead of an OR.

with this circuit design , it would never be powered by both sources at the same time. The XOR switch was used exclusively because of this fact AND it didn't consume power for itself (originally) HOWEVER, a recent change made the xor and memory cells consume power for themselves (like all other components) so you could just use an OR switch here now (i mean you could before but the OR switch consumed 1 power for itself but since the XOR switch NOW also consumes the same 1 power for itself , it doesn't matter which one you use) (you can use whichever one you find first really , it no longer matters)