The reason it only uses batpack, and not lap pack power, it due to IC2 tiers.
Batpack is tier 1, as is the batbox, and the IC2 miner.
Lappack is tier 2, as is MFE.
Advanced Lappack is tier 3, as is MFSU.
Ultimate Lappack (GT) is tier 4, as is AESU.
The batpack however has a very low charge...