Board Thread:Questions and Answers/@comment-72.227.91.253-20150108023452/@comment-25002135-20150108025222

When you evolve a unit, their BB lvl is reduced by half.

For example, when a unit has bb lvl 8, when evolved it is reduced to bb lvl 4.

In the case of odd numbers, the bb is reduced by half, rounded down.

Hope you find this useful.