This is a battery holder for a 4s pack of 26650 size cells. It consists of 3 parts.... a case, an inner support that holds the threaded inserts, and a cap to mount the switch, voltmeter, and power connector. I made this primarily for powering my Sound Devices MixPre-D, but you could use it for other stuff too.

If you don't want to use the Hirose connector, the hole will fit a coaxial power connector just fine. I've included an STL for the cap that has no cutouts, so you can make your own.

Parts list: 

• 8 6-32 threaded inserts on the part labeled "4s V2 Inner": (McMaster PN 93365A132) 
• 8 Button head socket cap 6-32 x 3/8in screws 
• 1 Mini rocker switch whose part number is "MINI1SW" (hole is 9mm x 14mm) 
• 1 Hirose connector part number: HR10A-7R-4S (hole is 8.5 mm diameter) 
• 1 Mini LED voltmeter (hole is 23mm x 15mm)