Electron P-MOSFET reverse current protection?

Hi there! First post so bare with me.

I have an electron which is to be controlling a bunch of solar powered equipment via a 12V lead acid battery.
The particle is powered through a 5V switching converter through Vin and ground tied to V- from the battery (I appreciate I could power directly from the battery at these voltages but I would like the extra protection offered by a decent regulator). All good, works great.

To protect against wiring up the battery wrong, I have incorporated a P-channel MOSFET which does the trick.
However, due how it is wired up, this then puts +12V on Vin and +12V on the Electrons ground.
Obviously there is no potential difference so I’m thinking that, at least in theory, this should be ok and cause no damage but I’m having second thoughts before I plug it in backwards to test and blow something up.
The Electron is also going to be connected to the included LiPo which is also tied to this ground thus potentially putting 18V though the system?

Honestly, all these voltages are confusing me. Is my thinking correct with this or am I missing something?
Is the value of ground voltage actually irrelevant?
Not wanting to blow up this expensive bit of hardware!

EDIT: Diagram below (U4 is the Electron)

Thanks a lot :see_no_evil:

You should fix a ground reference as the GND pin as perform measurements with respect to this pin.

Why don’t you just replace the fet with a diode ?

The P-fet serves as a diode but with lower voltage drop during normal operations :slight_smile:

True, but this is does not seem like a low voltage critical project where every ounce counts. Thus I was just curious why not just put a bridge rectifier there and there would be no issues.