Thanks for the great question. The battery in the Soundsport free headphones won't retain a 100 percent battery charge even when turned off. As the battery requires a charge, it will pull a charge from the case. So, if your case is not plugged in for a week, the headphones will eventually drain the power from the charging case.
The plus side is your headphones will retain a full charge, the downside is if you don't charge your headphones on a regular basis it will drain them eventually.
Tony - Community Support
My apologies, @jonat is correct I was referring to the Soundsport Free. The premise, however, is the same, the Sleepbuds will continue to charge even when the case is not plugged in.
Sorry for the confusion.