Solar panel, how do I know if it is bad?

I have a spotlight can and 2 days ago I noticed the lower dome light was blinking. I checked the device health and found the battery was low, 31%. I figured it would charge the next day but instead it continued to lose battery so I took out the battery and put it on a charger to see if the battery itself was still good. It did fully charge, though it took a long time. Is there a way I can verify if the soar panel is still good, or if there is something wrong with the spotlight cam charging circuit? Where I have the camera it gets plenty of sun and light, we have had this spotlight cam for a little over 4 years and have not had any issues until now. Thank you