All batteries age because the chemicals change over time, thus the charging and discharging characteristic will change. The remaining battery % can be inaccurate and that's why you should calibrate Omnicharge's battery when you first receive the product, and periodically in future. It's easy to do just follow these steps:
1. Step one: Fully discharge the Omnicharge until it stops outputting any power (make sure the battery is fully depleted - don't disconnect your device even if it says 0% on the screen). Press the Power Button once and you can see the 'Empty Battery' icon on the screen as shown below.
2. Step two: Fully charge Omnicharge to 100%
And that's it! Your Omnicharge's battery is calibrated.