Something

class Scene_Battle
  alias as_battle_atb_setup atb_setup
  def atb_setup
    as_battle_atb_setup
    for battler in $game_party.actors + $game_troop.enemies
      battler.adr_max = 10000
      battler.adr = 0
    end
  end
  alias as_battle_phase0 update_phase0
  def update_phase0
    as_battle_phase0
    for battler in $game_party.actors + $game_troop.enemies
      if battler.dead? == true
        battler.adr = 0
        next
      end
      if battler.adr > 0
        battler.adr = [[battler.adr + battler.agi + (battler.adr/100).abs, 0].max, battler.adr_max].min
      else
        if (battler.agi - (battler.adr/100).abs) <= 0
          battler.adr = [[battler.adr + 50, 0].max, battler.adr_max].min
        else
          battler.adr = [[battler.adr + battler.agi + (battler.adr/100).abs, 0].max, battler.adr_max].min
        end
      end
    end
  end
end

class Game_Battler
  attr_accessor :adr_max
  attr_accessor :adr
  alias as_battler_initialize initialize
  def initialize
    as_battler_initialize
    @adr_max = 10000
    @adr = 0
  end
end