Think that hole is a clip to hold the cables in place inside the downtube. On my Canyon there is a small plate under the downtube above the BB which you can remove to access the B junction and battery (although you need to insert it through the BB shell)
Think that hole is a clip to hold the cables in place inside the downtube. On my Canyon there is a small plate under the downtube above the BB which you can remove to access the B junction and battery (although you need to insert it through the BB shell)