As one of its daily deals, That Daily Deal offers the Pilot Electronics 5,200mAh Portable Battery Pack / Heat Pack for $14.99 with free shipping. That's tied with yesterday's expired mention and the lowest price we could find by $25. It heats up to 120 degrees and lasts for up to 3.5 hours. A Micro USB cable is included for charging. Deal ends today.
Before you spend another dollar on items and services like these, check with your public library. You will likely be surprised by what it offers for free.