Setting up the wiring and connections for a semi-portable battery-powered sound system proved a little confusing to me. There didn’t seem to be an easy way to make DC power connections between the batteries and the audio equipment. I was looking for a system which would allow me to have the batteries in one place and the mixer and amplifier in another, and that could easily be disconnected. Hand-building power cables and using ring terminals wasn't it. If you'll recall, the mixer needed 12V (and came with a AC to DC wall wart with a barrel plug) and the amplifier needed 36V.
The solution that I’ve hit upon finally involves the “SAE connector".
The SAE connector is "hermaphroditic", which means that the plug is also the socket - ideal for a splice-type connection. Also most of the cables available are color-coded, red for hot and black for ground, so it's a little harder to screw up. In practice, this means that from the battery you're looking for a connector with the female red terminal and male back (to avoid exposing hot), and from the device, you want the opposite. Make sure you use a wire gauge calculator to determine how much power is flowing through and how thick you need the cables to be - my calculations came up with 16AWG at least, for the amplifier at 36V.
On the battery side, I installed these ($12 on amazon for two), which came with ring terminals and an in-line fuse - perfect:
For the mixer, I found this ($8 on amazon), which is three feet long and has a DC adapter barrel connector on the other end. It plugs right into the mixer!
Now I just need to keep the 36V and 12V wires straight, and I'll be able to hide the bulky batteries away somewhere. Extension cables aren't hard to find, and they're pretty affordable.