2 grounds for 2 batteries in series monitoring circuits on 1 PCB

[YoTech]

My ideas is this. I know voltage is measured in paralel, so I have 2 batteries (12V each) in series. I connect 1 voltage monitor circuit to the upper battery's + and - (battery 2). I connect the second monitor circuit to the lower battery's + and - (battery 1). I need ground on the upper circuit and the lower circuit? The grounds must be separated? Can this be done on a PCB? Say 1 layer, internal copper 1 is ground 1, and botttom copper is ground 2. Do I have to connect the 2 layers toghether (star them) and how do I do it in KiCad?

I am a bit unfamiliar with the ground concept! I know the ground is just a low resistance conductor (10 on -7 ohms) which attracts electrons. It has a low reference potential (and generators are always grounded for defence). But what the heck can a small PCB layer do? Is there any point of putting 2 grounds on 1 PCB even? Should I use blind vias or normal ones? Whats the difference?

Sorry, its not many questions, its 1 question with all the details combined as 1!

 

[YoTech]

Here is the block diagram of the entire PCB with 2 circuits for monitoring each of the batteries connected in series. Please read the picture text in this post!

 

[(*steve*)]

Consider what will happen to the bottom battery if you ground both sides of it.

 

[YoTech]

Yes, that will be a short circuit or there will be no voltage from the battery, I understand. That means that the upper voltage monitor will have to be connected to the lower battery's "-" or a separate ground. In other words it must not be connected to the upper battery's "-" if there is a ground on it, and there must be no ground on it, if its connected to the upper battery's "-"? This means the PCB's layout should be layer 1 (top copper) used as signals with blind/buried vias only, layer 2 internal copper used as power supply copper fill, layer 3 (internal copper) used as signals with blind/buried vias only, layer 4 (bottom copper) used as ground copper fill.

EDIT: Thank you very much for all your help until now. Please check my other thread, which shows what will happen if the batteries are disconnected from series connection while the voltage divider is still being connected to the upper battery's "+" and lower battery's "-".

 

[(*steve*)]

If the grounds are not connected then you can't measure the battery voltages in the way you want to.

You need to draw a circuit diagram embodying the concepts in both of your threads. You'll either see that it's not possible, or you'll describe it more clearly so we can understand that you're planning something a little more complex.

 

[YoTech]

Here is the whole project:
https://www.dropbox.com/s/2yhe8vddfd2t4it/Battery.voltage.monitor.whole.circuit.pdf?dl=0