I am sorry you and your friend are having trouble with your E-Werke. It would be nice if they worked properly the first time. Despite Peter White's comment, I find it hard to believe your situation is unique. However, there may be a silver lining. Diagnosing this problem may help you and others. I too am looking to purchase one. I know someone who has one and likes it. He has it connected with a Schmidt NAB 28. I would consult him, but I believe he and his wife may be touring in Eastern Europe.
I have a few questions and a suggestion or two. What dyno hubs are you using with it? If you are using a Shimano Hub, do you have the proper voltage protection? Did you do the installation? If it was a bike shop, did they check the the way it was wired to the dyno hub? I know the E-werke has different voltage and amperage settings, are you sure they were set correctly? Did you run more than one device at the same time? When it stopped working, were the devices, they were charging, still working? Unfortunately, I am not sure that Peter White, has the inclination or the ability to test your devices and send them back to Germany for a proper evaluation.
I would make two inquires in Europe. I would write to Starbike.com. They sell dyno hubs and the E-Werke. Their staff are very knowledgeable, on these matters and may be able to help you come up with a solution. I also know their prices are a lot less than Peter White.
I would also contact Busch Muller in Germany. I am sure Peter White has their email address. It would be ashame to write off these devices without finding out the cause of the problem. If they were working and then stopped, then I believe something caused them to possible short out. Is there a fuse in it? If you provide me the answers to the above questions, I will try to research this and come up with an answer.
Sheldon Brown would have been an excellent resource but sadly died a few years ago.