Answer... found on TBeach KBase

<span style="font-size: larger;"><span style="font-family: Verdana;"><font size="2">Read below from TBeach KB, light goes OFF when 75%+ charged... so you plug it in, it flashes red a bit, realizes it is 75%+ charged and light just goes off... so when light is OFF it is good to go... although they say to fully charge... NO way I see to know it is 100% ?</font>
<span style="font-size: larger;"><span style="font-family: Verdana;"><font size="2"></font>
<span style="font-size: larger;"><span style="font-family: Verdana;"><font size="2">How to properly charge and re-charge the PX3 internal battery</font><span style="font-size: larger;"><span style="font-family: Verdana;">

<font size="2"> The PX3 features a lithium polymer ("Li-Po") battery, which is more reliable and should last longer than the older lithium-ion batteries. It's best to charge up your PX3 headset all the way before first use.

- Turn OFF the headset. (The LED is steady on when the headset is powered OFF. The LED will flash on/off when the headset is powered ON.)

- Plug the headset into the base/transmitter to charge for a minimum of 6 hours. You can charge it for up to about 12 hours.

- You can ignore the LED on the transmitter. The LED will go out when the headset is charged up to 75% of its capacity. Although at this point you could disconnect it and use it, the headset won't be charged up all the way. We recommend that you charge it up all the way and then use it. </font>