One module charges normally, but the other one doesn't charge in the same case. Does that mean the module is defective?

Not necessarily. The issue could involve the module, its contacts, or its charging slot.

Reseat the affected module and check that the contacts on both the module and case are clean and dry. If needed, gently wipe them with a soft, dry cloth.

Its corresponding indicator should turn orange while charging and green when fully charged, normally after about 90 minutes. If the indicator stays off or the module remains unresponsive after charging, contact support@neurorester.com with your order number and identify the affected module.