Grab a bunch of cells of that make, weigh them, find a typical number for AH per gram. For A123 I get 0.035 AH/Gram for their 20AH pouch cells, 0.033 for their cylinder cell.
IMO, A123 is top of the line, so generic LiFePo might be a bit lower. So say
30mAh/g typical.
Compare that to a computed 'theoretical max' from these sources:
mAh charge capacity of LiFePo on Wikipedia of 170mAh/g
Check that Wiki number:
Weight of 1 Mole of LiFePO4: 158g
Coulombs in 1 Mole (one charge per Li):9.65E4
Coulombs in 1 mAh: 3.6
mAh per mole of charge: 9.65E4/3.6 = 2.68E4
mAh per gram of LiFePO4: 2.68E4/158 = 170 mAh/g. Ha! Spot on.
mAh charge capacity of graphite sheet 372 mAh/g
Convert the two numbers to grams per Ah:
LiFePO4: 5.9 g/Ah
Graphite: 2.7 g/Ah
add, invert, to get
116 mAh/g of graphite and LiFePO
That is too high, of course. How are you going to get the current out? With copper and aluminium sheets. They weigh maybe as much as the anode and cathode, so divide by two to get 58mAh/g. That's closer to the real world.
A little more reading: I -know- you can not get all the Li out of LiFePO. Mr Borong Wu et all say you can only get about 0.6. So that means 102mAh/g for LiFePO, not 170. With that correction, I get 80 mAh/g for the materials alone. Add in the weight of the anode and cathode as before, I get 40 mAh/g. Pretty darn close!
I am interested in the answer to this question and, while I have read much on LiIon batteries, I have not seen it answered with certainty anywhere or addressed directly.
I agree with the intuitive logic of Ignacio's answer, but I think that he is probably incorrect in practice.
Practical information supplied to me by an experienced manufacturer of battery powered products is that the general experience of Chinese manufacturers of LiFePO4 based products is that LiFePO4 cells, which are similar but not identical in general chemistry to Lion, will degrade and die if constant float voltage is applied to them. LiFePO4 cells would if anything be expected to be more robust and resistant to adverse treatment than LiIon (due to the Olivine internal matrix which resists the mechanical degradation mechanisms which LiIon suffers from.)
It is generally advised that use of a lower terminal constant voltage will increase LiIon cycle life at the expense of lower absolute capacity per charge-discharge cycle. However, ALL LiIon charging algorithms and chargers that I have seen terminate the charge cycle at some point and remove the charge voltage. ie they never "float" the battery. Less aggressive chargers terminate charging when Ichg is say 50% or 25% of Imax, and more aggressive chargers charge until Ichg dropsto say Imzx/10, but none ever let Ichg trickle off to zero.
As allowing Ichg to drop to some very low value would maximise capacity and simplify charging it would seem logical that manufacturers would do this if it was acceptable. None do, that I have ever seen.
LiIon battery manufacturers all advise a minimum end of charge current.
Charger IC manufacturers typically offer several end of charge currents but none ever offer "float" as an option.
So, it seems highly likely based on the above, that floating a LiIon battery will cause premature degradation.
Best Answer
Cell maximum is 20 Wh. Battery maximum is 100 Wh.
Thus battery with maximum of 5 cells of 20 Wh.
As also explained further on.
Even though a powerbank might fit: "a single encased electrochemical unit one positive and one negative electrode".
You could probably throw loads of money on this debating over the meaning of the law in court. But safety will most likely win.