If I recall, then BLP is Battery Level Percentage, with a % at the end. Which I suppose is just a convenience for displaying text, as I'm assuming Facer's math processing gets confused by the "%" character (or wants to interpret it as modulo).
So all you really need to do is first get the percent with (#BLN#/100) and then multiply that by the max length of the bar, i.e., ((#BLN#/100)*26)