OXONO Portable Charger, Solar Power Bank 30000mAh with 2 USB 5V 2.1A Outputs, Compact External Battery Pack for Cell Phone Tablet Charging, Outdoor Camping … currently running as a Cyber Monday deal for only $16.99 – over half off!  There are a ton of these on the bottom of the Amazon page, so if these model doesn’t meet your requirements, check out the others.  I’m still carrying a spare battery from at least 10 years ago – – maybe it’s time to move into the 21st century.  Besides, I Iike the idea that having a solar option means no more TSTL characters in cozy mysteries.