Well, what a debacle!, the new battery is losing 5% capacity on each charge. I haven't the time to carry out extensive testing and to be honest, I don't see that an end user should have to do such things, either the battery is functional, or it isn't.

I made contact with Wannsee Electronics on eBay, they were happy to receive the faulty battery and replace it.

Sadly, the UK Post Office will only handle the old battery if it is fitted/inserted into a device, I cannot and am not allowed to send the battery as it is. I notified Wannsee about this, they have been very good and have stated that it has become too complicated to return it and are going to send me another battery anyway.

I have digested the comment about the battery possibly being a fake, but I have no easy way to tell this (except possibly by hours of testing using guides here on TMO). I have to take Wannsee at face value, they seem reputable as far as eBay sellers go and to be honest, despite their feedback showing negative comments mainly about Polarcell batteries, but none of them for BL-5J Polarcell battery, the majority are batteries for Samsung Galaxy phones and some Nokia Lumia.