Love the ANKER PowerCore 5000. Perfect USB battery pack for short trips. It's 5000mAh capacity is, for me, just about perfect as it will allow me to fully recharge from flat an iPhone 6S Plus and a Garmin 1000, all in one convenient little unit.

The PowerCore 5000 also utilises two different fast-charging technologies. PowerIQ provides the fastest charge to any device up to 2A. VoltageBoost increases output to overcome cable resistance and ensure a consistent top-speed charge.

The PowerCore weighs 135g, is 107mm long and 32mm in diameter which makes a it a very convenient size indeed and it's enough power to keep you going over a weekend, or a short cycle trip.

I reckon starting fully charged this little unit would provide enough power for say a three day bike trip. Coupled with the ability to charge it up during the day from a hub dynamo you could keep going for pretty much as long as your energy and imagination allows.