If your device is not holding a charge after a full charging cycle then your battery has likely reached the end of its lifespan. Rechargeable Lithium-ion batteries have a limit for the number of charging cycles they can go through, and as this limit is approached the battery will exhibit much a much lower capacity.
See heading "My device only works when the solar panel is attached" in the troubleshooting page at:
[[Fosera Scandle 200 Troubleshooting#Section_My_device_only_works_when_the_solar_panel_is_attached]]