Depends on how much I vape, obviously, and the particular battery. All my batteries get me through at leas a whole day but how much beyond that varies, and not in the way you might expect.
900mah ranges right at 1 to 1 1/2 days. 650mah gets me about 1/4 of a day MORE. 1100mah vv a bit less. Home made 1800mah is the one I use on days when I know I am going to vape heavy 1 to 1 1/2 (but the 2 parallel batteries in that were heavily used before being moved to that device).