Ok I'm a noob to all of this, I just bought a mbx7re and need a transmitter. Does any of the transmitters show how much battery is left on the car? I would like to monitor how much percentage is left. Is this option called real time view?

There are many transmitters with telemetry and can monitor other things besides battery.

I see on a lot of transmitters even on the knock offs, they have a low voltage warning/siren. Is this a siren/warning the car battery pack? Or the transmitter batteries?

Transmitter batteries

If you are worried about low voltage in the car you could get something like this, this is one example, there a few different types.
http://www.hobbyking.com/hobbyking/s...rm_2s_4s_.html