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Are all 18650 batteries rechargeable?

I have recently got a very nice 50 mw green laser. But now it is starting to get dim and flicker quite a bit. It came with 18650 battery. I measured the battery which is meant to be 3.7V but was surprised to see that it was in fact only 2.9V. I have figured out that it is the battery which is causing the problem. But I need to know whether the battery which I have is rechargeable or not? Is it rechargeable? It is in plain blue casing with Tian Lin 18650, 2800mah, 3.7V written on it. Can someone help? Also tell me whether or not all 18650 batteries are rechargeable? Thanks.