That means they are 2000 mAH @ 3.7 v nominal.
That will be at .5 or 1 Amp whereas a typical light will draw 3amps.
Honestly man, you run the risk of blowing your hand off, or worse. Its just not worth it using unbranded cells.
Chris
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Problem is you have no idea how much use those batteries have had.. They may be cheaper than brand new Panasonic 3400's but the won't be as high capacity and they could be on their last legs...
Edit: just saw Chris' post. Basically what he said