I rarely do product promotion. For my birthday I received a Lepow Moonstone 6000 mAh External Battery with Dual USB Ports for Smartphones.
I can not say enough about how amazing this back up battery pack is. It is inexpensive. It has dual usb ports for charging, perfect for charging your cellphone and your ipad at the same time. One usb port charges twice as fast as the other. You can get about six single rounds of a full charge out of it. It charges quickly and is small enough to fit in your purse.
I use mine all the time. I charge it when I get home and use it to travel. I highly recommend this product.