Solar Power failing?

Starting to think the Vue solar panel is not working anymore.
It needed a new battery in early April which was not that surprising as it was a year since the last replacement, but now it's showing Low Battery again - even during the day when it should easily run on solar power.

A known problem area is that the capacitor which stores power to use overnight can fail eventually, but that would show as a problem first thing in the morning.
I have a plan to fix up a VP2 I got cheap on ebay - it needs a Temp/Humidity sensor - and have ordered one from the USA.
Although rather pricey this will be better than any idea of sending the Vue to be repaired, although once the VP2 is up and running I'll see if I can do more diagnosis on the Vue.
The batteries aren't hugely expensive but replacing every other month would soon get tiresome!