It turns out that aircraft have a very sensitive centre of gravity that needs to be close to the centre of lift. If you were to design a "battery bomb" you'd have to carefully engineer the pre- and post-bombing centre of mass and ensure that your control surfaces can respond adequately. In addition, you'll need bomb-bay doors and associated mechanics which adds mass and complexity. All of this takes a toll of efficiency, cost and reliability. However, it's an intriguing idea, especially if you use steerable parachutes that can neatly fly themselves back home, maybe all the way into a recharging slot.