If you are the manufacturer or have close ties to them then this is what I recommend on product improvement.
1.) No detachable parts because those parts can be lost.
2.) I recommend that the batteries be replaceable. The option to buy new batteries from the manufacturer is a good idea.
Lithium Ion batteries only allows so many discharge from it so eventually the batteries need to be replaced. I have many of these solar items lying around that are useless to me now and the only problem is the battery that lost its ability to store charge.
3.) You want to make the product globally interchangeable with other solar products. For this reason, you want to make All connections to be USB to make it interchangeable with other solar devices.
Please check out Teslamaker or Lasersaber on Youtube. They used to have a website call Teslamaker.com
Their items was one of the best out there. All their solar units were compact and portable with no loose items connected to it. Their ideas was extremely revolutionary progressive. They made the battery for their solar kits interchangeable with powerbanks so as powerbanks improve so can your battery for their solar kits. Powerbanks are for charging phones and these banks are charged through USB.