When charging the transmitter (WL-T) from the receiver (WL-20 / WL-20L), connect the included USB cable and a commercially available USB AC adapter (5 V/0.5 A or higher) to the DC IN 5 V port on the receiver.
If the transmitter still does not charge, check the following:
BATTERY indicator blinks red
A charging error may have occurred. See the related Q&A "The BATTERY indicator on the transmitter is blinking red." for more information.
POWER indicator blinks red rapidly
The unit may require repair. If you are unable to resolve the issue, contact your local dealer or a Roland customer support (Backstage, Roland Account required) for assistance.
Using the WL-20 / WL-20L for the first time, or after a long period of disuse
The transmitter battery may be completely discharged. A fully discharged transmitter cannot be charged through the TRANSMITTER jack on the receiver. Use the included USB cable (USB Micro-B type) to fully charge the battery directly.
Charging from a USB AC adapter
Connect the included USB cable and a commercially available USB AC adapter (5 V/0.5 A or higher) to the DC IN 5 V port on the transmitter.
Note: When charging from the DC IN 5 V port, the wireless connection does not operate.