Good info - you included the "v2.0".
It could be software (now v2.1) - see DCDC-USB Mini Box PSU problem
I assume you have the UPS handshaking required (ie, DCDC says battery low please shut down - PC starts shutdown - Then it is shutdown so DCDC shuts down - Or DCDC may do a drop-dead shutdown; ie, "sorry dude, battery too low - I'm config'd to drop now" ["But I'm not ready you AC-DC wanabe!"... "Stiff! Complain to Admin!"])