One throttle wiring two controllers on two batteries

As the title mentions, I'm using one throttle wiring two independent controllers with two batteries, and the batteries are not common ground.
I've seen some videos that use one throttle wiring two independent controllers but with one battery.
So the wiring of the throttle goes 5V GND SIGNAL to controller1 and SIGNAL to controller2.

But how about two batteries?
How should the throttle wired?

(5V,GND,SIGNAL) (5V,GND,SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

OR

(5V,GND,SIGNAL) (SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

OR

(5V,GND,SIGNAL) (GND,SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

Thanks for your reply!!

As the title mentions, I'm using one throttle wiring two independent controllers with two batteries, and the batteries are not common ground.
I've seen some videos that use one throttle wiring two independent controllers but with one battery.
So the wiring of the throttle goes 5V GND SIGNAL to controller1 and SIGNAL to controller2.

But how about two batteries?
How should the throttle wired?

(5V,GND,SIGNAL) (5V,GND,SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

OR

(5V,GND,SIGNAL) (SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

OR

(5V,GND,SIGNAL) (GND,SIGNAL)
Battery1-------Controller1--------------------throttle--------------------Controller2-------Battery2

Thanks for your reply!!

from my perspective I would say 3) (5V,GND,SIGNAL) (GND,SIGNAL) is safest and should work best. 1) could blow one controller and 2) is missing ground is unlikely to work