I agree, make sure you have a quality cable. I've used both charging places -- plugging into the USB with the other ports or the one in the bin. I have trouble keeping it at 100% all the time but I'm usually also listening to audio books and running a GPS logging program on it. Besides whatever else it thinks it should do... Hunting for wifi takes a lot of energy, so I try to remember to turn off wifi before anything but a very short trip.
Of course, if it's not showing charging, it's not charging. But even if it is, either the source or the cable may not be up to it. Get a good cable first. They may look the same, but they are not necessarily! If you charge with a cable in your house, try that one.
Ours also has the pad charger, but my phone gets pretty hot on that, so I don't use it much.