The Advanced Batpack, or Adv.Batpack as it is referred to in the game, is an upgrade to the BatPack added by IndustrialCraft 2. It stores ten times the amount of power as the BatPack.
In order to charge it, place it inside something like a CESU. If you use a tool that is in any stage of discharge, using it with an Advanced Batpack equipped will charge it as much as the Advanced Batpack can (full if possible).