kenneth house
Looking at the Secura patent for battery charging you will notice two things of interest. The method was based upon a Ni-Cd battery charging profile, and the procedure assumes a trickle-charging phase of indefinite end following the fast charge phase.
Interesting. The NiCd 'trickle charge' mode that Boeing employed on previous models was also referred to as the T-R (Transformer-Rectifier) mode. Basically, once the battery was charged, the charger switches to a constant voltage source, both to keep the battery topped off and to supply the few small loads always connected to the battery bus. Without this mode, the battery would cycle between a constant current charge (high speed) and slowly being drained down by these parasitic loads. Since there was a requirement to maintain a high state of charge, this could not be tolerated. The odds that, when the batteries standby capacity was needed it would be at the 'bottom' of one of these cycles, were not acceptable.
Does the 787 system have such parasitic loads? Stupid question actually, because the batteries own built in charge monitoring system is one instance. But then, does the 787 system have such a 'float' mode to avoid this state of charge cycling and the inevitable low points in the capacity curve?
Its possible that the only way to fly with a LiCoO2 is either to provide the float voltage (unsafe) or to accept the lower point on the available charge curve as the 'best' avalable charge for design/certification purposes and thereby have to oversize the battery to allow for it. One would need to peek inside the head of the systems engineer responsible to know how this decision was made, I'm sure.