Just wondering if I could pick folk's brains about the most appropriate power source for a two-ish week trek? I just need something to keep an Android smartphone running (no other devices). I plan to put it in "ultra battery saving" mode, switch off wifi, bluetooth and mobile data etc. I'd be using it for the odd text, phone call and photo, to check the weather forecast (temporarily re-enabling mobile data), and using the Kindle app in the evenings. (I had planned on taking my Kindle Paperwhite but saw on a different thread here that that isn't the most weight-efficient option). At the moment I only have a 2000mAh powerbank (weight ~ 80g), of the type given out as marketing freebies at business conferences. I'm worried about relying on this though. Do I need something better? Sorry for the basic question - I've never used anything like this before!