I had a Juicebar, has a battery in it. A surprise rainstorm killed it. Given that I camp for upto a month at a time it was my first branded unit trialled in the British summer. Left out all day, hoping it doesn’t rain, it can keep up with old phones power needs, just. It cannot produce enough power to recharge a smartphone. Sending texts, using 3g for uploading pics and browsing the web, and you’re stuffed, power drops drastically in your phone.
If you’re going away for a weekend only then I recommend you simply buy an extra battery, or two, turn your phone off at night and restrict 3g usage to “necessary”. Search fleabay for the cheapest proper ones. You could get one of those large battery cases, but beware that recharging phones chews up non-rechargeable batteries and you’re going to end up dumping them in a landfill.
If you can carry weight, then a building alarm lead acid battery, female cigarette lighter socket and whatever you need from there works.