I would guess that reliabilty is more important than weight - but that's up to you. I have been very happy with my Anker portable power supply, as have many. They come in many sizes, shapes, colors (and weights).
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I got this one and it holds a bunch of charges for my phone but its a tank. Bulky and heavy. Overkill for anything less that a 7 day trip.
All of the anker products i've owned, are durable and have a long life. I always carry at least one of their little 5000 mah units, just in case. It's good for one full cell phone charge.
However I think this 10000mah model is the best price/weight package. It's 2.3 full phone charges which should be plenty for 4-5 days if you are on airplane mode, and only 7.5 ounces. I don't have a zoleo but my garmin in reach will last for 4-5 days on a single charge as well.
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