Yamaha TW-E3C True Wireless Earbuds (Red) - Manual (Page 15)

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NOTE
( You can also charge the earbuds while the charging case is charging.
(
You can charge from the USB port on your computer instead of using a USB power adaptor.
(
Once you place the earbuds in the charging case, the indicators on the charging case will show the remaining battery power for five
seconds (except when the charging case itself is still charging).
15
Charging and Powering > Charging the charging case