Shimano GRX RX 815 Series Dealer's Manual page 86

INSTALLATION/REMOVAL
Installing the battery
3.
Connect the electric wire to the battery.
(1) Check the electric wire that will be connected to the battery.
(2) Connect the electric wire to the E-TUBE port of the battery.
* Be sure to push it in firmly until you feel a click.
(2) E-TUBE port
(1) Electric wire
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