I have 3 (varying sizes) from New Trent, and I would definitely recommend them. They hold their charge for weeks, and they're strong enough to charge my phone, Kindle, or camera. I think New Trent may be a little more expensive than others (I probably gave $50 or $60 for my most expensive one), but I've tried a few of the $10 or $15 ones and they didn't stay charged long enough to be of use when I needed them.
This is my biggest one (but I swear it wasn't that expensive when I bought it. I gave $60 in June, 2013. I wouldn't dream of giving $200 for one): http://www.amazon.co...ailpage_o07_s00
This is the one I use the most, and at the time of purchase it was $32.95: http://www.amazon.co...ailpage_o07_s00
Edited by Bopeep, Oct 12, 2015 - 12:23 pm.