The core of the system is an inexpensive single-stage solar charge controller. No, solar is not required.

This kind of controller is used because:

• it is cheap
• it is very compact
• it can prevent overuse of the battery
• it has USB outlets
• it allow panels to be added if desired

Here is how they are wired:

• the SOLAR terminals will be left empty if one has no panels. If you have panels those wires plug in here. A 20A controller has been selected so one could run up to 200w of 12v panels with this setup.
• the BATTERY terminals connect to whatever your battery is: starter battery for single-battery systems, the aux battery for dual-battery systems
• the LOAD terminals are where you take your 12v power from. This is critical because the controller can be configured to turn that circuit off at a predetermined voltage like 12.7v; this is called a Low Voltage Disconnect (LVD). Your battery cannot be drained when used this way.
• the USB output is also controlled by the LVD.

One might use a $10 adapter like this one, cut off the single male plug and insert the wires into the LOAD terminals.¹⁾

Users with more complex power needs might wire a fuse panel to the LOAD terminals and from there to the various loads.