Long ago I had this idea. I was going to use a Surefire weapon light and an Eotech 553 and then all I would need is CR123 pattern batteries to run them. I would then be able to use rechargeable CR123s and save money.
This was before I learned first hand how bad Eotech sights are. I also contacted Eotech and Surefire and asked about rechargeable batteries. I got a hard NO, with terms thrown in like, “melting”.
A CR123 puts out 3 volts. Some of the RCR123 can be charged to the point where they are putting 4.5+ volts each. Put a pair of those in an electrical device that is not designed for it and you might cause catastrophic failure. So that killed my plans back then. Fortunately that got me into Aimpoints.
Now, a good bit more battery powered devices are designed to use rechargeable batteries, and there are new sizes of batteries. A little while back I sold several older lights and I picked up a Surefire M600 Dual Fuel light that uses a 18650 rechargeable battery. It can take 2 CR123s for a slightly lower output, but one rechargeable 18650 out performs them. Now, there is also the Zenitco Perst-2 which has an Green Laser, Slaved IR Laser, IR Illumination, and a 740 lux light that uses the 18650 battery. One battery could run a high performance Surefire weapon light or a Perst-2 combination device.
This just seemed awesome to me. I sold a bunch of older stuff to update to this new versatile configuration.
But then those bastards screw me. Turns out, that the 18650 battery is a very loose standard and almost each company making them makes them different lengths.
Over on the Candle Power Forums there is even a chart made by HKJ about it:
Manufactures can never make this simple. What a mess.