Everyone wants a battery that is small and light, but there are compromises, especially if the margin for failure is narrow for critical missions. When calculating battery size, the fleet user should consider two factors:  allowing for spare capacity to provide for unforeseen activities, and  anticipating capacity fade that occurs naturally with the age of the battery. Equipment manufacturers tend to ignore the fading aspect when calculating the required capacity and base the service on a new battery with full capacity.
The acceptable capacity performance range of a well-managed battery fleet is 80 to 100 percent, meaning that packs that fall below the 80 percent threshold are replaced. Allocating 20 percent fade in addition to a 20 percent emergency reserve would reduce the usable battery capacity to 60 percent. Such a large reserve for a worst-case scenario may not be practical and battery users go for more leniency. A battery analyzer plays an important role in battery management in that the batteries are checked every one to thee months to ensure they all fall within the anticipated performance bandwidth.