Batteries are among the heaviest payload the balloon must carry. Batteries, further, are the only payload which absolutely require any sort of heating during the mission. As a result, it makes a great deal of sense to enclose the batteries separate from the rest of the components, and include a system which can selectively ballast batteries. The compartment for the batteries must have a hinged bottom, on a spring-loaded system. When the batteries are released, they weigh the door open, and drop from the balloon stack. In the intermediate time, the compartment remains closed and insulated. After a majority of batteries are released, the battery compartment itself should be ballasted.
This all requires the intelligent control of a battery controlling microprocessor. The charge status of each pack must be monitored by this battery controller in order to drop batteries with low charge before batteries with full charge. In order to facilitate this, there must be 2 or more battery bus lines. Each battery pack must include circuitry which allows any pack to be connected to any battery bus at any time. The logic of the microprocessor must ensure that one, and only one pack is attached to each bus line at a given time. Each battery bus line must have voltage and current sense circuitry. This can be easily accomplished with a small number of transistors included on each battery pack. These bus lines must be combined and regulated to 12v, 5v and 3.3v.