Hello Curly,
Perhaps I also need to clarify, or you need to take another look at my post...
When a laptop or cell phone or other electronics product manufacturer offers a rechargeable Li-Ion battery in their product, there is research, development, and testing done to make sure it is safe to use, and will work fine in their product. They take the time to address the "What if" questions and engineer ways to deal with them.
When you take batteries from a laptop and use them in your flashlight,
you have to address the "What if" questions and find your own ways to deal with them. A fireproof container and attending to the charge, we have found, work very well.
When used properly, Li-Ion cells work great. The danger comes when you don't use them properly, either through abuse or a lack of knowledge of what is involved with using them. Li-Ion cells have a lot of energy stored in a small area, so the effects of something going wrong are greater than when something goes wrong with a NiCd or NiMh battery.
Safety and danger are the reasons you are unable, in the US, to run down to the local hardware store and buy single Li-Ion cells.
Let's look at this a little closer...
Unless the flashlight is designed around using Li-Ion cells, we are pulling a cell from one service and using it in another. Some of us do a lot of testing to see if we think there are any problems, but we find that there is a lack of engineering data on many brands of cells, and little published test data.
A Li-Ion cell, while rapidly venting with flame, can see temperatures exceeding 1000 F. This is something we all want to avoid. I am sure you are aware of the laptop battery issues and recalls. We have also heard a few reports of cell phone battery issues. So far, the power tool batteries seem to be "issue" free, although those in heavy use have moved to a safer chemistry.
Now you may think this is stretching the example a little far... but that has never stopped me before.
Will a laptop computer run from several cell phone batteries hooked up together? Yes. Is it safe? Probably not, but I think we need more testing to make an educated guess...
Protection circuits on cells are supposed to be a secondary safety. Your circuit design is supposed to control the cell within its safe parameters. If your main circuit fails, the protection circuit kicks in avoiding the rapid vent with flame incident. If your flashlight and charger rely on the cells protection circuit, you have lost a layer of safety. Will it still work? Yes. Is it safe? You have to decide that.
The picture I keep in mind is that of a road flare. After the initial rapid venting, a Li-Ion cell will burn in a fashion similar to that of a road flare. If you don't mind lighting a road flare, setting it on your dining room table and then going to bed, you should have no problems charging Li-Ion cells unattended.
I use Li-Ion cells all the time. I don't know about your particular lights, but I use them in lights that are not specifically designed for use with Li-Ion cells. I also have a laptop and a cell phone and power tools that use Li-Ion cells. I invest in good quality chargers, have a charging area that may not be flame proof, but is flame resistant, and attend to the charging. I test my cells to make sure I am using them safely, and periodically check them for their state of health. I almost never charge Li-Ion cells or battery packs overnight, unless it is outside of my living area.
I don't think you need to become paranoid about using Li-Ion cells, but you do need to understand the safety issues involved. If you have a family, they need to also understand the safety issues and have a plan of what to do if something goes wrong.
By all means proceed with your venture into using Li-Ion cells, but do so with caution and understanding, and take a moment to consider safety.
Tom
