This works great for trickle charging my truck battery, but I’ve just learned how to use it as a USB solar charger.

.If you buy a 12v power (cigarette lighter) extension with two or three outputs, you can plug the solar charger into one socket, and a car USB adapter into the other(s). You don’t have to plug anything into the cigarette lighter

Power will flow from solar panel into one socket providing power to USB adapter in other socket.

I have purchased different kinds of solar chargers from other makers (not this Eco-worthy model, so far) that actually WARPED from being on the car dashboard in the sun! But as for this charger, so far so good. It does put out power, whether it’ll be enough to prevent the battery from running down remains to be seen. I wanted to know if it was working, so the first thing I did when I got it was to measure the power coming from the charger with a VOM meter (I had to do this because I have gotten other chargers that are DOA out of the package). I found that it does make power. Of course it makes more power in bright sunlight, (about 30% more) and it also makes power even in overcast weather.

A fair question might be why would anybody need this at all? The answer is modern cars use battery power even when they are just sitting. This power is used to keep alive the memory in the radio and the car’s computer. Even though the power used for keep-alive is very low – in the milliamps – this power can be enough to run down your battery if the car sits idle for a week or longer. Some people even disconnect the battery of a car that sits a long time, which does work to keep the battery from running down. However the computer memory is gone, so if you disconnect the battery, the car would need to be driven quite a while for the computer to reset for the “smog test memory” (the best description i have, for certain functions the computer stores, and that are the first thing they look at during a smog check), Long story short, if you have a state smog check coming up soon – the LAST thing you want to do is disconnect the battery! Since it won’t pass smog until those functions reset.

Anyway I measured the voltage on the cigarrette lighter socket and got nothing. I put the VOM on all the fuses with the dial set to check continuity and they were all good. Rather then open that can of worms trying to fix it I just used the supplied clips to put on the battery. Then ran the power cord out of the engine compartment and through the door frame of the passenger side, and closed the door on it. And set the charger on the dash, where it gave me a reading from the alligator clips as shown in the image.
By the way, the panels are covered by plastic when you get them and just remove the plastic for it to work optimally, if you use a sharp object use care not to cut the panels.

Update 9/21/2017 I have been using this solar panel for several months now, haven’t had the battery run dead yet so it’s still working. I bought a second unit and installed it the same way – just routed the cable out the engine compartment and into the cabin and close the door on it. The alternative is chopping a hole in the firewall to fit the cable through and I don’t want to do that, I’d rather have to change the cable once in a while if I have to. I guess the only way I’d find out if the cable is too worn is to measure the voltage at the clamps from time to time other wise it might stop charging and I wouldn’t even know it.