Adafruit powerboost 1000c not working with battery


I bought a powerboost 1000c for a battery powered project but it doesn’t work with just a battery connected. When I connect the mains it will work but not without it.

When the battery and mains are connected sometimes (not always) the charge light and full charge light comes on but when I disconnect the mains the device powers off. If I hook up the lbo (low battery output) to a led with a resistor (with mains and battery) it lights up along with all of the other lights (power, charge, full charge and lbo).

Does anyone have any idea what is wrong and how I could fix it?