I just bought the Omars portable power bank on Amazon. This thing is a beast and with a 24,000 mah capacity it can charge all three of my Spark batteries five times over. The real treat about this unit is it has an AC connection so you can literally power any household device up to 80W, incredible! I use my 3 battery charger dock from the fly more kit and this way I can quickly charge my extra batteries while still being able to fly. This thing is a bit larger than my 22,000 mah USB power bank but the weight is almost the same. It also charges itself from empty to full MUCH faster in about 4 hours compared to my USB power bank which takes around 7 hours. With this unit you can charge 3 batteries, your controller and phone/tablet all at the same time! The price to performance ratio is better than anything else I've seen. This is an excellent piece to add to your field kit in my opinion.