TX2 Battery Power Requirements

The module and development board uses DC DC converters, which means they draw more current if the voltage is lower.

The module is specified as 5.5V minimum. I imagine that any conforming power control circuitry will assert power bad and shut down if the voltage goes below that.

If you’re using a LiPo straight into the Jetson, I suggest you use a “low battery alarm” to save the battery from over-discharge; LiPos discharged below 3.0V per cell are dangerous to recharge and dangerous to use after re-charge (and, in fact, if they over-discharge, you may not be able to re-charge them at all, even if you’re willing to live dangerously.)
For example: Amazon.com