IRIS makes a lot of products focused on document management, including OCR software and a range of portable scanners. The IRISPen Air 7, which costs $/€149 (£109), measures 3.5cm by 13.97cm by 2.5cm, weighs just 28g and has a rechargeable battery. The specs on the product website don't divulge how long the battery lasts, but the promotional video mentions five hours. The device charges via an ordinary USB cable, and you probably carry one of these as a matter of course.
IRISPen Air 7 review at ZDNet.com
IRISPen Air 7 review at ZDNet.com