Hi guys, I was wondering if anyone had any experience with one of these:

It says you just have to plug it in and power the phone off and on again. But when I try to turn it back on the S4 refuses, it displays the battery symbol with green dots under it and vibrates once, then cycles doing that in a loop. I've tried using a 1A power source as well as the stock charger but to no avail. I know it's chinese rubbish but the exact same thing is on amazon and seems to have worked for other people with an S4.

I've tested it with a cheap tesco tablet as well, it took longer to start up but ignored the fact it was plugged in at all. Neither charge when plugged in when the devices are already running.

Any ideas? If not can you guys recommend anything else I could try that's available in the UK?