Thank you, Mach
The whole battery thing reminds me of many software and iPhone/Droid folks that always want the latest and greatest apps.
No doubt that the Li-ion batteries have a greater power/density/weight capability than some of the not-so-old batteries like the nickel-metal-hydride ones. Funny, but Toyota sticks with those nickel ones for their Prius.
In a plane that weighs as much as the 787, a few pounds for an "older", but more safe battery seems a good trade-off.
My friends who served in the 'stan and Iraq told me war stories about those "new" batteries. The temperatures and charging systems did not help, so they went back to older batteries.
In my mind, it ain't worth the extra battery capacity to require expensive charging systems and such. Then there's the requirement to have a good fire extinguishing system if one of the suckers goes into thermal runaway.