According to this battery comparison sheet, lithium-ion batteries should have an energy density around 110-160 Wh/kg. Wikipedia cites it may be around 100–265 Wh/kg, although it refers to it as "specific energy" and uses "energy density" to refer to a measurement based on physical volume.
I'm thinking of buying a lithium-ion battery pack rated for 12V @ 6800mAh, giving it 81.6 Wh, and it weights 162 grams, meaning its energy density is 503.70 Wh/kg. Since that level is nearly twice the documented energy density for lithium-ion, is my math wrong? Or are the battery's specs incorrect?
This is somewhat related to this question, but I'm trying to calculate it from a real battery's specs, not the technology's theoretical limits.