Actually I'm using this product from past 3 years and now also it gives good backup
Loved it. It successfully charged my oppo f1 without heating it. But I guess its output is around 9000 mah as it drained out completely after charging my cell for 2.5 times. But I'm happy with its function as even Samsung power bank used to overheat my cell for which I couldn't use it for charging purpose. Also a year warranty is commendable too.
product is not good under 4000 mah do not buy this product...