What's the difference between NCR18650B's and NCR18650A's?
Energy density and therefore, capacity. Simply put, they put more chemical goo in the A's than they do in the B's.
I reiterate that since these are not high drain capable batteries, their use is limited to devices that will not exceed 5.0 amps in current. For those devices, better choices exist in Panasonic's NCR/PD or CGH/CR cells, which have current ratings of 10.0 amps.