NeoThermic:
If i have my grounds linked (there is a wire connecting the arduino ground pin and the negative side of the battery PRE regulator) do I need to worry about too much current flowing through my arduino's ground pinI have a few MOSFET controlled higher power LEDs etc which will take 100mA each. The intention is that the current will flow from the regulator, through these devices, through the MOSFET gate and down to ground of the battery, without ever passing through the arduino itself.
Will this happen? Does linking the ground to the negative achieve this? Thanks in advance!
Yes, under normal circumstances the current is going to take the most direct pathway available to the lowest voltage in the circuit. Now in some situations a reverse current is possible, but that's usually due to either something going very wrong in your circuit (e.g. a part failing or a combination of shorts) or outside factors like a current induced by a very strong external electromagnetic field. A diode between the Arduino's ground loop and the negative terminal of the battery will offer some protection from the latter by blocking any reverse currents large enough to potentially damage an Arduino that are induced in the rest of the circuit.