3.0V RCR123s are not all their cracked up to be, they are usually either 3.7V li-ion or 3.2V LiFePo4 cells with voltage regulators in them to try to keep the voltage down around 3.0V under a load....
The problem is this:
1. The voltage will usually be higher than you get from 2x primary CR123s, some lights are fine with the increased voltage, but any direct drive light (like a incandescent tactical) is very likely to blow it's lamp on 3.0V RCR123s.
2. The capacity is not going to be as good as expected, most of em deliver UNDER 500mAH, in some lights, that means about 1/3rd the runtime compared to primaries, keep in mind, that the voltage regulator in the cell, reduces space available for the actually storage portion of the cell, and also, is only so efficient, some percentage of available power is lost to heat in the regulator.
3. It's not always clear WHAT it is you are getting, and you shouldn't dive into using li-ion cells unless you know for sure what you are getting and how to properly use and maintain them. Some RCR123 3.0V cells are simply labeled li-ion, when they are of the LiFePo4 variety and require a different charger to use correctly.
There's probably more to it than that that I am forgetting at this point in time.... But I would seriously look at each light you are planning on switching to rechargeable on an individual basis and pick out appropriate configurations for each light. In many cases, you can AVOID cells with voltage regulators, by matching standard li-ion protected cells to proper bulbs, or certain LED drivers...
For example, if you had a 3xCR123 style light, you can pretty much directly replace that configuration with 2 17500 sized li-ion cells, if you had a 2xCR123 sized incandescent, you might be able to swap to a 3.7V lamp and run a single 17670 sized li-ion cell.
So... what lights do you want to convert?
