Charging batteries from solar panels

Do you want a light detector in the circuit that switches from solar to battery power? An opto-isolator circuit can do this, but I see a complex circuit for this idea.
Short of a manual switch or timer, the solar panel can feed a voltage regulator that can shut down on low voltage input and automatically switch the device on.
Your little critters will get a mild jolt, not a death shock, that should train them to move on to another easier target.

You know they like beer, right? https://www.wikihow.com/Use-Beer-to-Get-Rid-of-Snails-in-Your-Garden

and, apparently to shock them, all you need is copper wire:
https://www.telegraph.co.uk/gardeni...Eight-ways-to-get-rid-of-unwanted-snails.html