I just purchased this how long does it hold a charge?
This FAQ should help:
How long will the charge in a PowerCore 20100 Portable Charger last without being used?
Generally, our external batteries’ static power consumption is so low it would take between 20 and 36 months to drain completely. However, It is also worth noting that the powercore’s chemicals will become less active if left unused for extended periods. To extend your powercore’s life, please discharge and recharge it at least once every 4 months.