9V battery clip with 5.5mm/2.1mm plug : ID 80 : $2.95 : Adafruit Industries, Unique & fun DIY electronics and kits
Battery Clips (Pack of 5)
Amazon.com: VWEICYY 9V Battery Connector,10 PCS T-Type 9 Volt Buckle Connector Hard Plastic Shell Used in Student Experiment,or Other Equipment with Battery(T-Type, 10PCS) : Electronics
Coin Cell Testing Clip with Cable For 300MA CST Battery Analyzers only - MTI-CST300-CLIP