Shimano GRX RX 815 Series Dealer's Manual page 77

INSTALLATION/REMOVAL
Installing the battery
Long type (temporarily installing the front of the battery mount)
Tighten it together with the bottle cage using the mounting bolt included with the
frame.
2.
Adjust the position of the battery mount and bottle cage so there is
enough space to attach and remove the battery.
The figure shows the short type, but performs the same position adjustment for the long
type.
Attach and remove the battery to check the space.
Mounting bolt
(temporary)
Bottle cage
Battery mount
108 mm
77