The cheap ebay charger I bought and the two hong kong batteries I bought are still working great. I can't tell the difference between the hk batteries and the real Nokia one in practice, though maybe if I timed them closely there would be a difference.

There was a problem, though. The cheap charger came with ANOTHER battery, that looked like a real Nokia battery. It was so exactly the size of my battery slot that I had a hard time getting it out of my N800! In the process of getting it out I damaged it and never used it again.

No one on this forum has reported an exploding battery of any kind.