I got a Bikeray battery off ebay to replace an old tired Dealextreme one, it seems good- hasn’t done anything unexpected, lasts well, came in a good case too. But haven’t taken it apart or anything.
Trouble with DX batteries is just uncertainty- I have a couple of batteries from different lights sourced from there, both claimed to be the same spec, one is good, one is not- they don’t control their supply chain so you can buy 2 identical looking lights and get different batteries, never mind 2 different models. So it’ll always be a gamble.