I had my new brushed basically stock E-Maxx out for her first run last Sunday & I'm a little confused about the "low voltage warning" .
Is this supposed to warn me & if so .. how ?

Does it beep when a certain value is reached ?

Does the light on the ESC simply turn from green to red ? If that's the case , it doesn't do a lick of good with the body on .

I'm running a pair of 5400 mAh Venoms at 20C 2s
There was a point toward the end of the run & she seemed "sluggish" and once I pulled the body off , the LED was red .

What ESC are you running? Some had the old EVX that was made by Novak, others have the newer EVX2.
I have owned both models of the EVX. I know that in setup, the red & green lights also tell you what type of batteries you are running. RED is for NICD or NIMH & GREEN is for LIPO's. If it slowly blinks red, then the Low Voltage Output has kicked in. Here's a link to the EVX2 manual to help you out.
https://traxxas.com/sites/default/fi...ctions_WEB.pdf

Thank you very much for the PDF link .
The ESC is the EVX-2
So , reading this it states that at a certain threshold it will shut down .
I'm a little concerned that mine didn't .
It got a bit sluggish & the light was red .
Or did I just not go far enough for it to reach that threshold & cut out completely ?

If the LED was RED when you started playing, then you have the ESC set for NICD's or NIMH. If the LED was GREEN then you have then ESC set for LIPO's.
The ESC will blink red when the low voltage cutoff turns on.

The Low-Voltage Detection circuitry constantly monitors the battery
voltage. When the battery voltage begins to reach the minimum
recommended discharge voltage threshold for LiPo battery packs, the
EVX-2 will limit the power output to 50% throttle. When the battery
voltage attempts to fall below the minimum threshold, the EVX-2 will shut
down all motor output. The LED on the speed control will slowly blink red,
indicating a low voltage shutdown. The EVX-2 will stay in this mode until a
fully charged battery is connected.
Your model includes a Power Cell NiMH battery. The EVX-2 speed control’s
Low Voltage Detection has been disabled for best performance with
this battery. The speed control’s LED will glow red when it is turned on,
indicating Low Voltage Detection is disabled. Be certain to activate Low-
Voltage Detection if you install LiPo batteries in your model. Never use
LiPo batteries while Low-Voltage Detection is disabled.

Thanks again bud .
And yes , I did set it up per the instructions & the light was solid green before the run .
Excellent . So everything I experienced was "normal" .
Good news !

Glad it worked out for you!