​I have charged my Note 4 about 6 times without recharging the battery and has 34% charge left. It takes around 7-9 hrs to fully charge the battery.

Battery itself is very heavy. Im happy it does the job intended.

Just a thought, but if you're buying this for a phone with a removable battery, don't bother with it, and just buy some spare batteries instead. They're an order of magnitude lighter, smaller, cheaper, faster, far less cumbersome to use than one of these.

Packs with a 12v output are much more useful

£15.99 prime now?

forgot to say above..... £17.99

Just for information really, I bought this one at Amazon. 20000mah, dual usb port, high power output 3.5V. Very happy with it. Some will find it a little heavy to carry in a pocket but fine for a big bloke like me. Perfect for camping etc as 3 phone charges so far for me has barely depleted the power pack at all.
Amazon power pack

I purchased this one the other day. 50000mah with display for £13

http://m.ebay.co.uk/itm/External-50000mAh-Power-Bank-Pack-Dual-USB-Battery-Charger-For-iPad-Mobile-Phone-/182245678706

I have this and it's about twice as big and heavy as my brother's equivalent from Anker. Still, it's okay for sticking in the car for an emergency.

Sainsburys appear to be having a clear out at the moment.

TPLink powerbank @10400 is around £16-00 and the 15600 model is £24-33

https://www.amazon.co.uk/gp/product/B00J03VYXK/ref=ox_sc_act_title_1?ie=UTF8&psc=1&smid=A28QVT3E6UV0FU

Slightly lighter and best seller for £1.20 more.

Lightweight tends to suggest low quality/capacity batteries within. But then again it's kinda subjective.