Battery holder : Li-Ion 18650 Battery Holder (1S1P) With 2.6" long 20AWG & PCB (1S1P-18650)
2-Way 18650 Battery Holder | The Pi Hut
Amazon.com: Adeept 2Pcs 2 Slots 18650 Battery Holder Case with Wire and 2.54mm JST Connector, Batteries Connected in Series 7.4V, Solderless Battery Storage Box Holder for DIY Projects : Electronics
3-cell 18650 Battery Holder - Solarbotics Ltd.
Amazon.com: 2S 18650 Battery Holder Case Box with 6" Wire Leads for 2X 18650 (8V) Li-Ion Batteries by Envistia Mall : Electronics
4-Cell 18650 Battery Holder – HandsOn Tech
Amazon.com: RuiLing 5-Pack 18650 Battery Holder 3 Slots x 3.7V Battery Storage Case DIY Batteries Clip Box with Pin : Electronics