No. Only through mains. I had the same thought but after using some of the tablets that charge via USB I changed my mind. A lot of them charge really slowly via USB which means that you cannot charge them and use them at the same time (if you are at 10% and plug it in to charge it will still die if you keep using it). They will run out of battery. At least with mains power this is not an issue (1A x 5V = 5W, 12V x 2.5A = 30W, 6x faster charging). Also I found out you can get 12V /5V battery packs which I will probably get later on which can charge laptops. These are a bit bigger but they can then charge anything.
