Battery Left is highly dependent on consistent usage. For me, it was very inaccurate because some days I'm busy and won't do anything on my phone until I get home, but some days I can check Facebook/email/whatever.
However, that's not really the point. Even if you have pretty consistent usage, the point is really that the 1% increments - which the OP was looking for - are both only estimates, and are not nearly accurate to 1%. They just can't be. Your usage isn't robotic, it's organic and changes. So, while BL is a great widget, what the OP wants - 1% increments of battery life - isn't available.