Micropuck LED driver gets really hot
Micropuck LED driver gets really hot
  [...]
  3.7V 750mAh LiPo Battery



As others have said, 3.7V exceeds the allowed input voltage for the MicroPuck LED driver in the typical "boost" configuration.

Worse than that, according to the MicroPuck documentation / datasheet, the Absolute Maximum Rating for input voltage in that configuration is 3V. Using the usual interpretation for "Absolute Maximum Rating", that means that by connecting more than 3V (e.g. perhaps 3.7V or more, depending on the state-of-charge of the battery) you might have permanently damaged that MicroPuck, even if you now try to use it in a valid configuration. :-(
However, the good news is that the LEDdynamics, Inc. 2009 Micro Puck Application Note COM-DRV-2009-APP "Additional Applications of the 2009" shows an alternative "buck/boost" configuration where the document explains:


  
    This topology boasts an extremely wide input voltage range that will continue to supply effective power as batteries become exhausted, but is 15% less efficient than boost.
  


Here is the original diagram from page 4 - see the document for more information.








(Original source document)

As you can see, the allowed input voltage range for that MicroPuck buck/boost configuration is 1V to 7V, which includes the voltage range (e.g. 3V to 4.2V) for a single Li-Po battery which you mentioned (although with a reduced efficiency compared to the boost configuration). However, as I explained above, that original MicroPuck might already be damaged, due to the input over-voltage in the "boost" configuration.