I am looking to buy a Losi 2 cell li-po for my Tek 18, this batery will drop in perfectly, The battery says voltage regulator required. Is that the same as a the cut off in my Quark? Thanks in advance, I am new with li-po.

A regulator is needed if you are going to use this pack to
power your servos in a gas car/truck.

To further answer your question, No, it's not the same.
The voltage cut-off feature, 3v per cell, or 6v for a 2c lipo is to
prevent an over discharge and subsequent damage to your pack.
The regulator is used when powering servos with a 7.4v or even a
11.1v lipo pack, because only 6v with 5 amp draw is all the power
needed for this application.

Thank you.