As an "outsider" I have so far resisted the temptation to post. However there seems to be a dire lack of understanding of fundamentals.
As an aside, the Bentley Arnage motor-car(carries 1 driver and 3/4 Pax.) has 2 batteries of~ 60 AH capacity. When parked, the "standby load" ( electronic "memories" and the like , is provided by ONE battery.
In an infrequently -used car, this gets discharged such that Central-Locking ceases to function...BUT the second battery has capacity to start the car and then all warning, self-check, courtesy-light-systems etc. come on -line POWER PROVIDED BY THE GENERATOR- which also , via a split-charge system, recharges BOTH batteries.
What's so different?- except the Plastic Fantastic sosts a few million more AND has 3 alternative power-sources as well as 2 batteries.
In both cases, system-power is generated "on demand" the batteries are purely a reservoir of energy to get a generator started. I'm astounded at the fact that a huge, power-hungry beast such as this, has such miniscule reserve-supplies, but there again, the chance of 4 main gennys + 2 APU gennys + a RAT genny (which "should" supply enough power to kick the APU into life) makes the need for big batteries superfluous.
As I've stated previously in other threads, the model helicopter world are early adopters of Li technology...these people WILL invest a couple of weeks' wages in a flying-machine which may well catch fire, have an electronics glitch or otherwise self-destruct.
THE RISK IS MINIMISED BY PROPER CELL-MANAGEMENT.
You note I did NOT say "Battery" Several other posters have pointed out - the charger MUST monitor EACH cell continuously.
Discharge is done also via an electronic circuit that eliminates out-of design- parameter excursions.
I find it difficult to understand why Boeing has not arranged their batteries and associated controllers on a modular basis...It should be feasible to" un plug" the battery/controller packs from the aircraft's main harness and substitute with an alternative Certified battery/controller pack......
Oh, Wait.... they had absolute blind faith in the unproven technology and didn't bother to make an alternative strategy, "just in case"
Regarding the "can't add weight, otherwise everything will demand a few extra pounds"-argument,- RUBBISH There isn't another on-board system with the KNOWN risk of unexplained spontaneous combustion .
These Lithium cells are the ONE issue where there are still unquantifiable risks.--Composites, you say?... plenty of light aircraft, racing-yachts and cars have come and gone and a huge database of knowledge has been aquired.
The Airframe is not the problem, nor the brakes, entertainment systems or aerodynamics....
Electricity and it's storage is the achilles heel of this aircraft and until it's sorted, the Press will have a field-day and feed sensationalist horror stories to the revenue-generating Pax.
Re-load-limitations.... Is the airframe Really load-limited by Pax+ luggage? -or are the majority of flights conducted mixed pax/freight.
Obviously, were one carrying lead-ingots, weight would be the consideration, but freighting, say, flowers, you run out of volume long before weight becomes an issue (other than balance )
Please don't all jump on me at once!