Dry firing an AEG
 

I have been told it is bad to dry fire (both empty and with a dead battery), and I'd like to know why.

Puts more stress on the mechbox shell. When there's a BB in the chamber it provides back pressure on the piston, reducing impact force.
Breaking the front of the mechbox shell due to dry firing was a far more common issue back when everyone had a weaker mechbox shell. Still not a good idea, but it's not nearly as dangerous as it was 6 years ago.

NiMH, doesn't really matter. They'll just roll to a stop and aren't capable of outputting enough amperage to damage your motor at low voltage.
If the NiMH is right dead, and you keep drawing current till it's right empty, it can actually reverse polarity on you.
LiPo's that are approaching 3.0v/cell can be damaged by going under that voltage.
And once a LiPo reaches critical low voltage (where your gun starts to slow down) the motor starts drawing more amperage, which can damage electronics or the motor windings. This is especially dangerous in systema PTWs.

It's fine. You'll dry fire it every time you run a mag empty or clear it in a safe zone.

What's not OK is watching Blackhawk Down with it in hand and joining in all the gun fights. That'll add some wear.

Ah I see, just for clarity I have a 9.6 nimh in a g&g f2000.

Just wanted to make sure that going click click wouldn't destroy my gun.

Actually no back pressure in airsoft guns. The force of the spring is going to slam the piston with the same force. Once the bb is pushed past the hop up nub, it practically rolls out of the barrel.

In a springer pellet gun, back pressure exists because the pellet skirt maintains a continuous seal in the barrel until it leaves it.

^^^^^ I've never seen that image before thank you

What are sugarsofters?

Doesn't everyone get out their favorite gun for watching action movies tho? Guys?

Hah you're not alone. That's when I lot of gun maintenance is done

and a lot of gbb mag baseplates get broken too hehe

Never.

Turns off Flashpoint and puts P90 away...