Hi, I'm done with my project, and the last problem I wanna solve is about the power source.
I don't have a charge controller, I wanna know if I can directly connect the solar panel (17v max when directly hit by sun light 1.5W) to the 12v battery? Someone in arduino group on facebook said that it should be fine to do this.
Hi,
What are your battery specs?
Tom.... 
hello tom. Here's the specs of the panel and batt.
The other question is how much the load is. 1.5w is not much power. Bare in mind that the rating will be generous. Also take int account that you will not get this power all day, there is a bell shaped power curve. It also changes over the seasons and there are cloudy days.
Instead of worrying about the charger first, work out how much you actually need then run your device then workout how much you need to charge the battery with the above considerations.
You may have already done this but most don't take into account theses things.
Weedpharma
That is a 1.3Ah battery and your solar cell can produce 0.64 amps at short circuit. That would be 49% of the capacity (0.64 / 1.3).
If there was no other demand on the power that would quickly overcharge that battery so a charge regulator would be needed.
...R
Reading the specs, that is a 10W panel.
No, you cannot connect that panel directly to your 12V 1.3Ah battery without using a charge controller.
In full sun connected to the battery you will produce around 500mA @ charge voltage, almost 7W.
To directly connect a panel to a battery the panel should output no more than 10% of the battery capacity.
So for your 1.3Ah battery that would be 130mA about 1.7W. Anything over that a charge controller is needed.