Originally Posted by
peter we
The APU is required for the ETOPS certification, which by definition has to be very reliable and therefore needs a very reliable battery.
Remember that the business case for the B787 was predicated on an increase in "point-to-point" journeys as compared to the traditional "hub-and-spoke" system. As such, it does not - at least initially - require ETOPS certification as it can fulfil that business case via intra-continental routes.