Battery Types ??

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Ok when I think I know everything---???Surefire primary batteries say SF 123A my aw 18650 says li-ion rechargeable and the theres ICR 123 and RCR and IMR etc . I need something to read and understand which tells me why 3.7 v batteries are not all the same and when someone says you can use 2 x 123 3.7 v but not rcrs 3.7 v what does this really all mean? I,m really in the dark on this. Help and thanks too.