I'm a little surprised about the following sentences in the G1 preview :
The DMC-G1 uses the brand spankin' new DMW-BLB13 lithium-ion battery for power. This battery packs 9.0 Wh of energy, which is pretty good.
What surprises me is that 9.0 Wh is considered a pretty good amount of energy for the battery for such a camera. Especially if it comes from a Li-ion battery.

Let's just compare to a "standard" set of 4 Ni-MH AA (LR6):
We have 1.2 volts (let's consider 1.1 Volt to account for the tension drop when the batteries go flat or disabled), and between 2 and 2.8 Ah per battery, that is between
4 * 1.1 * [2 ; 2.8] Wh or 8.8 Wh and 12.3 Wh.
A AA battery has a diameter of 14.5 mm and 50.5 mm height ("http://en.wikipedia.org/wiki/Battery_(electricity)") that is a volume of ~2.65 cubic centimeters. The packed energy density is then ranging from 0.8 to 1.2 Wh per cubic centimeters.

I really wonder how much smaller than 4xAA could the G1 battery be and how many what per cubic centimeters it may contain to deserve such a good comment as "pretty good". Especially considering than Li-ion is considered a much better technology than Ni-MH ? Does anyone has a clue about that ?