How can I charge 12V Li-ion or lead acid batteries using a solar panel? I also wish to interface the three, i.e. the Arduino, the solar panel and the battery, together so that the Arduino is basically driven by the battery but as the battery discharges, the solar panel would charge it. What circuitry do I need? Also tell the specifications of the solar panel.
There are lots of circuits for charging a SLA battery from a solar cell. You need 14.4V input, so you need to ensure that the output of you solar cells is going to be at least 14.4 for enough hours to charge your battery. This means you will need to know the output current of your charging circuit and do a fair bit of maths.
Charging a lipo battery will probably be more tricky. I would look at using a USB to LiPo charge regulating circuit and then generate a constant 5v from you solar cells.
You could also look at getting a COTS solar charge regulator, that allows you to connect the cells, load and battery and it does all the hard work for you.