I've had no problems with the actual battery, just that it arrived, after six weeks of waiting, with a cracked end cover and when in use the connecting cable suffered two solder joint breakages.
From your photograph it looks like the Rosenberg is now also used on the battery pack itself (this wasn't the case with mine, just the bike frame) so they may be using the same lead as the TEC pack. This is very robust lead so, as long as they actually deliver, you could be looking at a very useful product.
Using this extender gives you a battery of 600+ wh and I get about twelve to fifteen miles extra out of it which makes the bike just about perfect.