18V/5W solar panel to trickle charge a 12V car battery?

I'm running a small Arduino project out of an old 12V car battery (that was on my car since 2008 till 2015). I also have a 18V/5W solar panel.

Can I connect them together so the solar panel charges the car battery? The Arduino project is really really low on consumption so even a trickle charge will be enough to keep it running "forever" with the help of 1-2h of sun per day.

Thanks!

Answer

With a conventional solar setup, solar panels charge deep-cycle batteries. A charge controller is used to prevent overcharging and correct voltage and current. Car batteries are for a surge of current to start the vehicle. I'm not sure if a conventional charge controller could charge your battery correctly because deep cycle and car batteries have different chemistry. But from what I found Here, you should be able to.

I would just try it with a charge controller, or try to make one. Just experiment with some different setups and find something that works for you. Also, I don't know if 5w could power your battery because it depends on the capacity and the current draw from the Arduino.