Please understand that I am not an attorney nor do I consider this article to be an in depth discussion of the topic. I will provide links to more comprehensive discussion of the topic. I am merely trying to share some information that may or may not be useful and of interest to you.
In the marketplace today are many rechargeable batteries, available in different sizes and different chemistries. I would like to give you a glimpse into these offerings, along with the safety considerations and benefits of each type.
The first type to consider is the most prolific chemistry. The NiMH rechargeables are made by several manufacturers available from many retailers in several popular formats (AA, AAA, etc). You will find these to be direct replacements for alkaline batteries and can be used anywhere the alkaline is called for. These are very safe batteries to use and offer performance that will rival that of most alkalines. You will find them to be more expensive upfront than the alkaline, but I find that over the life of the battery, they are actually a much better value. The Sanyo Eneloop is considered to be a premier performer in this category as they offer excellent performance and long shelf life.
The real focus of this discussion is the rechargeable lithium ion battery. There are several different chemistries available here, I will focus on two – the LiFePO4 (lithium iron phosphate) and the LiCO (Lithium Cobalt Oxide). First and foremost, these batteries are not forgiving of mishandling! If not properly cared for, they can explode very violently! I will cover some of the safe handling considerations. Also, please realize these batteries are only intended to be used in LED flashlights, not incandescent! If you use one of these in an incandescent light, you will blow the bulb (best case) and probably smoke any electronics within the flashlight, voiding any warranty offered by the manufacturer. PLEASE DO NOT USE THESE IN INCANDESCENT FLASHLIGHTS!
Surefire has resisted the approval of Lithium Ion battery use in their flashlights. There are many reasons for this, but they have recently approved the use of a K2 brand of LiFePO4 rechargeables in their LED models. You will find these to be a safe battery to use in any flashlight or device that uses a CR123 battery. They have circuits built in to prevent the dangers of over-charging or over-discharging and match the required voltage of a Surefire light perfectly. The one downside to consider is the runtime is somewhat reduced. You will get about ½ to ¾ the runtime from this compared to the normal Surefire CR123 non-rechargeable. I use these batteries in flashlights that get a lot of use and keep extras fully charged on hand, readily available. Surefire recommends using the K2 charger when charging these batteries.
The real workhorse is the LiCO battery. This is the battery found in your iPod, iPhone, rechargeable tools, etc. You may remember some of the recalls in the past of these batteries exploding and products being recalled. These kinks have been worked out for the batteries installed in consumer products like the iPod, however, if you are not careful when purchasing a LiCO battery, you can fall into the same traps. When using LiCO batteries, please make certain all batteries in the device are at the same state of discharge. If one battery is almost fully discharged and the other(s) are fully charged, an explosion can result. Also, these batteries do not behave well when exposed to high levels of heat. Do not leave a device in your trunk on a hot, sunny day with this type battery installed. The upside to these batteries is excellent performance, both in terms of voltage delivered and length of life. Again, upfront cost is a little higher, but over the life of the battery, you should realize significant savings, of course, depending on your usage. Many of the new flashlights on the market today have what is called a turbo mode, which is a higher level of output. On most of these lights, the LiCO battery is required to take advantage of this feature. However, run time in turbo mode is very limited and high levels of heat are generated, so use wisely. Circuits are built into AW brand batteries that will allow the light to run at the same output level through the life of the batteries. How many times have you used a flashlight that started fading when the alkaline battery approached a state of discharge?
AW is the brand of LiCO battery to consider purchasing. It is available from some online retailers or directly from AW. Nitecore makes an excellent charger with protection circuits that will charge the LiCo and NiMH batteries. Do not use this for LiFePO4 batteries!
When purchasing Lithium Ion batteries, I recommend you only consider a few brands, be a battery snob, if you will. There are so many battery manufacturers out there, you really do not know what you may be getting in terms of a safe product. The K2 brand is the brand I recommend when considering LiFePO4 R123 batteries. AW is the brand I recommend for LiCO batteries of any configuration. AW is available here: email AW, to buy AW. You may find you can save a little money by purchasing a different brand, but when considering the safety compromise you may make, I think these savings dimish rapidly in attractiveness!
For a complete discussion of Lithium Ion battery handling, please consider this link: Candle Power Forum thread. I find www.candlepowerforums.com to be an excellent forum for everything flashlight and battery. For everything battery: Battery University.
I hope this discussion has piqued your interest in the world of high performance flashlights and batteries. Again, it is not intended as a complete and through discussion.
Please direct any questions to Ben and he can forward to me.