Three runtime claims, one pack, in watts.

FNB58 inline at the USB port · 37 Wh pack, two cells, verified by the charge test · the meter reads at 5 V and the pack is 3.7 V, so watts are the fair comparison

Lights on, awake

–W

282 mA at 5 V

Lights off, awake

–W

145 mA at 5 V

The pack

37Wh

10000 mAh at 3.7 V

What each claim needs the board to average, against what it drawsneeds · measured

32 h · CLOSE, AND A THREE-DAY RUN AT FULL BRIGHTNESS SAYS CONSISTENT 500 h · NEEDS UNDER A TENTH OF A WATT, DRAWS NEARLY TEN TIMES THAT STANDBY OWNS SLEEP, AND SLEEP KICKS IN WITHIN 60 MIN. THERE IS NO THIRD STATE

282 mA and 145 mA at 5 V on the FNB58 are 1.41 W and 0.725 W. 37 Wh over 32 h is 1.16 W, over 500 h is 0.074 W, over 1000 h is 0.037 W. Draw on battery may run a little leaner than at the port, which is why 32 h gets the benefit of the doubt and 500 h cannot.
Sleep draw not measured; the longest sleep timer the software allows is 60 minutes · CK Tech Check