These two plug-in hybrids will get battery upgrades soon.
The BMW uses Samsung SDI cells and Porsche uses Sanyo/Panasonic.
BMW i8 battery: 96 x 3,7 V x 20 Ah = 7,1 kWh
In October last year I already knew that the plugin hybrids that use Samsung SDI cells would get upgrades.
Now Autocar confirms that BMW will replace the 20 Ah cells in the i8 with 26 Ah cells that are already used in BMW X5 xDrive40e.
This will give the BMW i8 the same 9,2 kWh battery used in the BMW X5 xDrive40e.
But BMW could get bolder and jump forward even more.
Samsung already has newer 50 Ah cells for the plugin hybrids. They have the same volume and are made specially for replacing the older cells.

When BMW decides to replace the cells in the i8 with the latest 50 Ah already available, it will make a 17,8 kWh battery. Then it will get the full $7.500 EV tax credit in the USA, available for plug-in cars with 16 kWh batteries or more.
Autocar also says that an all electric version is being tested, which is good news. It will probably get the same 94 Ah Samsung SDI cells used in the recently improved BMW i3. Or even the latest 120 Ah cells. Either 94 Ah or 120 Ah cells will give the BMW i8 a good range since it has low weight and great aerodynamics.

Regarding the Porsche Panamera S E-Hybrid, it has a battery made with 104 cells from Sanyo/Panasonic.
104 x 3,7 x 24,5 Ah = 9,4 kWh
This car will get a smaller upgrade to 28 Ah cells already used in the Porsche Cayenne S E-Hybrid, this equals to a 10,77 kWh battery.
Porsche should surprise us and make an all electric version. Kreisel Electric already proved it works and made a 85 kWh battery for it.

The current battery technology already reached a level of cost and energy density that makes hybrids nonsense. The only thing that is lacking is motivation to build good electric cars, technology isn’t a valid excuse anymore.
More info:
http://www.autocar.co.uk/car-news/new-cars/all-electric-bmw-i8-works
http://www.topspeed.com/cars/porsche/2018-porsche-panamera-ar162807.html
https://newsroom.porsche.com/en/products/world-premiere-of-the-porsche-cayenne-s-e-hybrid-10757.html
http://press.porsche.com/news/release.php?id=776
An all electric i8 would be awsome…
A touch out of my price range though…
Panamera 4 E-Hybrid (2017) will jump to 37 Ah cells, resulting in 14,1 kWh. Not 28Ah-cells.
See for reference: http://www.autozeitung.de/auto-neuheiten/porsche-panamera-4-e-hybrid-2016-preis-technische-daten
Thanks Ralf K, I was just about to write an article about that upgrade.