Watch the numbers to see if they change at all.
It might just be a completely dead cell.
Without a good cell, it can be hard to verify the board is working.
I would replace the cell and then see what happens.
You can load test the box with a 24 volt 150 watt light if you feel comfortable doing that.
You can use (2) 12 volt 75 watt lights in-series to load test the box using the cord from the cell.
There are 2 black and 2 white wires in the cord; if you connect both white to one side of a light and both black to the other side, that should provide a test load at 24 volts and 150 watts = 6.25 amps.
Cut both white and both black wires and use the wires from the plug side.
Note: Do not do this if you have any doubt at all.
Only do what you feel 100% sure you know how to do safely.
Do at your own risk.
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