Need help choosing correct solar panel

hoghunter41 said:

So a 20w solar panel would put out around 1.25amp given the 75% figure you just gave  me? That would be 1.66amps x 75%= 1.25 amps per hour from the 20w solar panel if i'm correct?  Down here in Texas we get anywhere from 8-10hrs of sun on a good day, or normal day.

No, not at all. Solar panels aren't rated at 12.0V, they are rated at the voltage at which they output their highest amount of power. For 12V panels that are worth owning, that will be equal to or higher than 17.0V, assuming we are talking about current panels, not stuff from the 1970s, 1980s, etc. The cheaper panels, what we call "poly" (short for polycrystalline, but are also called multicrystalline) are pretty close to 100% of the time rated at 17.0V to 17.5V. Divide 20 watts by 17.0V, and you get 1.17A. Divide 20 watts by 17.5V, and you get 1.14A.

That 1.17A is what you will end up getting 75-77% of, before wiring losses, and before charge controller losses, and before battery charging losses. That means that a 20 watt @ 17.0V panel can only give you 0.8775-0.90A for an hour per day, at solar noon. And since there are so many losses, as outlined above, you will be able to put 50-52% of that 0.8775-0.90A into your battery, during that one hour per day. You'll get enough power to put some charge into a battery from it for longer than that, but not for much more than 7 hours per day, and only that much in July. Chasing the sun helps get a few more hours per day of charging, if you have unmounted panels, such as your 20 watt panel.