Get batteries that you can find the amp rating for, otherwise you'll never know if you're safe using them or not. Also, mAh rating doesn't say much in itself, even when accurate. For 18650s, batteries such as the Sony vtc5 (2600 mAh) and the LG he2 (2500 mAh) have more of their capacity in the useable 4.2-3.5v range than higher capacity batteries such as Panasonic's 2900, 3100, and 3400 mAh. Try to find tests and discharge curves.
No name batteries might be OK or even good, but as reliable information isn't available you'll never know.
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