Place a small piece of plastic from a filter on the negative side of the battery holder.

The negative side is marked with (-) and is on the side towards the solar panels.

Insert the battery with the correct orientation into the battery holder.

Secure the battery with a zip tie.

The zip tie is inserted from the front, just below the "sigrow" text and goes around the battery and through the PCB again.

The zip tie is then sequred with another zip tie.

Cut off the remaining parts of the zip tie.