Obtain USB power supply, plug into a laptop, and set output to 5.9V

Check the voltage with a voltmeter (you may have to set the power supply to ~5.8V for the voltmeter to read 5.9V)

Plug in the green terminal block from the power supply into the Open-Storm board solar port.

Confirm the solar charge LED is off.

Plug in a dead battery to the battery port. This step will not work with a charged battery

CAREFULLY turn the silver potentiometer next to the charge controller IC with a small flathead screw driver until the charge light turns on.

Although the screw has a phillip screw head, using a phillip screwdriver may damage the potentiometer. The hole in the center is too shallow for most screwdrivers. It is easier to use a flathead screwdriver!

Resource: 1. How to Select MPP Voltage on a Solar Charge Controller 2. Sunny Buddy Solar Charger V13 Hookup Guide