I have a Macbook Air (Haswell, i7, 8GB). I've spent the past month in Poland and while in my apartment I've been using a USB modem (Huawei) to connect to the Play 3G network in Warsaw. When using the modem my battery life on a full charge drops to about 8 hours, while when I'm in a coffee shop on wifi or just at home without the modem on, it goes back up to 14-15 hours. Does a USB modem really drain close to 50% more battery? Next time I'll plan to get a wifi modem, since charging my laptop every day gets to be annoying, when I bought it for its battery life.