Yyyyeeeeeeaaahhhhhh...that's not quite right.
In a traditionally wired AEG the battery negative goes to the negative side of the motor and the positive side of the circuit is completed through the trigger contacts. Usually this is a simple copper wiper type switch which makes when the trigger is pulled. Particularly with upgraded weapons with a high current draw this basic type of switch can arc which leaves carbon deposits on the contacts which results (ultimately) in failure of the trigger contacts. A "MOSFET" is in fact a type of transistor. This transistor acts as a power switch and is where the device fitted to AEGs gets its name from. Basically the circuit takes the wiring from the battery away from the trigger contacts, these wires are then replaced with smaller wires. The trigger becomes a low voltage switch and the transistor in tthe MOSFET unit delivers the power directly to the motor. This removes the likelihood of arcing at the trigger contacts extending their lifespan and also has the benefit that a MOSFET transistor has a much sharper ON/OFF transition than the metal trigger contacts which gives you a better trigger response. Unless your trigger contacts are particularly poor a MOSFET is unlikely to give you drastically higher rate of fire though.
More complex MOSFET units have additional functions such as active braking eg the Gate NanoAB (which forces the motor to stop spinning resulting in less overrun) or can be programmed to give burst fire eg the ASCU 3.
Unless you're going to seriously upgrade the power of the weapon or you are having an issue with overrun then you probably don't NEED a MOSFET unit, but they are quite nice if you intend to get one with flashy extras.
I need to know about the battery and deans connectors.
