yes i get the same, here is an example input file that the program says does not contain battery values. Maybe a verson problem with battery-syatus ?

battery-graph % more tst.txt
[Jul 20 08:50][00:35] 36.0%
[Jul 20 16:26][08:10] 36.0%
[Jul 20 16:31][08:15] 36.0%
[Jul 20 16:30][00:00] 98.0%
[Jul 20 16:35][00:05] 97.2%
[Jul 20 16:40][00:00] 97.2%
battery-graph %