I tried my batteries when the AVE mentioned it. They all gave a different code and I do wish I knew what it meant. 9.0s didn't give any code.
If the different light columns are positions in a four digit code, four flashes are a new code, and it doesn't light a column means a 0: (this is a guess)
1.5 0001 1087 0129 2070 (bat markings: B22LD 064159 130828P)
2.0 0101 0703 0126 3215 (bat markings: E53DD 102756 140527Y)
4.0 0101 0130 0027 3279 (bat markings: E54DD 785363 140928V)
5.0 0101 0315 0049 3546 (bat markings: G29DD 067296 151121G)
I'm not Alan Turing, but I don't see a correlation to the build date. Milwaukee paid to stamp the build date into the housing in an area it wouldn't wear, so they've got that covered. Its gotta mean something else.