So all the batteries are on the belly and a door opens up in flight when they get heavy and they get yeeted? Now you need to have sensors and actuators and inspections on all these doors. The cost of the plane just meaningfully increased.

Mechanical systems experience failure, so now your pilots need to train on the procedure for a stuck drop pod door. It'll probably change the flight characteristics and fuel efficiency while stuck open, so any time that happens it is now an emergency. That just added some operational costs for stranded passengers. You also would probably need a whole new cert for the airframe for any changes to your drop pods.

Throw them in little nacelles under the wings? Now slipping it onto the runway gets harder, more pilot training. What's the procedure for a battery pod strike? More training and more procedure and more certification. More redundant safety systems.

Throw them in the wings themselves? Now if the drop doors get stuck you really have a suboptimal flight condition.

I don't doubt that the technical challenges are surmountable, but all these considerations could literally double the cost of operating a plane compared to just accepting a lower MTOW. The military does all this crazy stuff because it's a hard mission requirement and they don't care how much it costs.