Testing Solar Chargers ?

[mr. buck]

I have some solar chargers on my feeders that are getting up there in age, roughly 8 years old. Some are starting to get clouded over look but really nothing that looks like corrosion. Is there a way to test the solar chargers to see if they remain fully functioning? Or do I basically just put new batteries in alll my feeders then monitor battery life to see if the chargers are doing their job? Thanks in advance for your responses.