did your kracken come with a large 8.4v battery originally? stick it in and measure how much space you have left.
then, take your 8.4v battery and look at it. it's orientation is 3 cells x 2 rows plus one sideways at the bottom. since 9.6v is 1.2v more than an 8.4v (assuming it doesn't say what each cell is) measure out what it might look like with 4 cells x 2 parallel rows.
edit for reference
Note the difference: