A few things you guys need to know about 3 Volt Li-Ion cells.
Before the advent of small (as we use in lights) LiFe cells, there were only LiCo cells that had diodes incorporated within the cell, to in effect, reduce the
working voltage to somewhere between 3.2 and 3.6 Volts (ie.
NOT 3.0 Volts). Due to the fact that these cells have diodes within their circuitry, a higher charging voltage is required to supply the 4.2 Volts to the base LiCo cell. This means that a
proper charger for 3 Volt LiCo cells has to charge the cell to 4.4-4.5 Volts to achieve 4.2 Volts at the underlying LiCo cell. It's important to note here, that charging a LiFe cell in one of these chargers, may not be so dangerous, but charging at this voltage level will surely damage the cell, more than likely sooner, rather than later.
Charging a 3.7 Volt LiCo cell in one of these chargers will not only damage the cell, but very likely could go 
. Most 3 Volt LiCo's have a maximum discharge rate between 1 and 2C.
Most of the 3 Volt Li-Ion cells you see around nowadays are LiFePO4. These cells supply a very similar voltage under load as the 3 Volt LiCo's, between 3.2 and 3.4 Volts (again,
Not 3.0 Volts). LiFe cells require a lower end voltage than LiCo 3.7 or 3.0 Volt cells. The end voltage is about 3.6 Volts for LiFe and chargers are usually rated 3.6-3.8 Volts, so these cells require yet another
totally different charger. Most of the smaller LiFe cells that I have, or have seen available, are rated at a maximum discharge rate of 1C, not very high. While A123 Systems LiFe cells (and others) are rated at 30C discharge and beyond, again, most CR-2 and CR-123 LiFe's I've seen, are not. Personally, I've been running 350mAh LiFe 123's sometimes, at 3C, but I don't expect them to last 2000 cycles either. It's probably pertinent to add that putting a heavier current load to a LiFe cell than it is designed for, is not nearly as dangerous as doing so to a LiCo cell.
So, there are three different types of chargers involved with Li-Ion cells. In some cases, you can use the wrong charger and get away with it, the cell just won't achieve full charge. In the worst combination's, you will either damage the cell, or run the risk of "venting with flame".
You have to use the proper charger for the chemistry/voltage of the cell you are charging. If you're not sure what chemistry you're dealing with,
contact the dealer or manufacturer.
As far as whether your light can use a certain cell, you have to find out
exactly what chemistry the cell is, and then I would contact the manufacturer of the light, and ask them if that is a suitable solution. Then, make sure you purchase the
proper charger to charge that chemistry/voltage cell.
Dave
