Are you referring to the SoundSport Free headphones charging case? If so, the 2nd and 4th LED flashing pattern will indicate battery error. But, do you always charge the case with the same USB cable, or does this change from time to time? I'd recommend always charging using the provided USB cable.
Also, I'd recommend visiting the Bose Updater to push the latest firmware to the buds and case. To do this, visit the website HERE and follow the instructions. Let me know if you notice an improvement or if you continue to run into errors when charging the product.