Hi beny, and welcome to CPF!:thumbsup:
Most small Li-Ion cells have a ridiculous capacity printed on the label. Lithium CR2 primary cells have a capacity of around 800mAh. LiCo/ICR Li-Ion cells generally have a capacity around half, or a little better than half that of primary cells. So at best, you're looking at 400-450mAh for a LiCo Li-Ion CR2 cell. These cells are hard to find, as well.
I use generic Chinese LiFePO4/LiFe/IFR (all refer to the same chemistry) Li-Ion cells in my CR2 Lights. These test out at about 200mAh under a 300mA load, typical of a small pocket light on "medium". As info, these have "800mAh" printed on the label, LOL! Performance isn't that great, but they work well enough for a pocket light. If you really need maximum runtime though, you'd be better off sticking with primary cells.
Also, be aware that not all lights intended for CR2 lithium primary cells will work with Li-Ion cells. LiCo cells have an open circuit voltage of 4.20 Volts and a nominal voltage under load of 3.6-3.7 Volts, which is considerably higher than the ~3 Volts of a primary cell. This is why I went the LiFePO4 route. These cells charge to 3.60 Volts, and under typical load run about 3.2-3.3 Volts. The lights I use them in run a bit hotter on "High", but seem to work OK. No doubt it stresses them a bit though.
Really, if you want to run Li-Ion cells in a light, it's best to get a light that is actually designed to run Li-Ion cells. The voltage specs for these lights will usually say "4.2 Volts", as opposed to a light designed for lithium primary cells which spec at "3 Volts". The use of Li-Ion cells in lights not designed for them could burn up the driver circuitry and/or the LED. Again, be aware of this.
Dave