Of all the Thinkpad Stack modules (including Wi-Fi router, hard drive, Bluetooth speaker) that I reviewed, the one that found a permanent home in my backpack is the 10,000 mAh Power Bank battery. It holds enough juice to recharge my phone, DSLR, etc., several times over, and when not in use, retains its charged state for a long time.
I keep the battery in my backpack with the charger cable already in place, so I can pretty much just attach the phone (or other device), zip the pocket shut, and get on my way. Within 10 minutes, the phone is charged enough to hold a decently long conversation.
Because the Power Bank charges the same way a phone does, via a micro-USB connector (it charges other devices via a full-sized connector), I simply flip the cable and use a car charger to top it off. It’s the one thing I make sure I charge when I’m traveling. –Jon L. Jacobi