WELCOME TO CPF!!!!
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Expect about 1/2-1/3 the normal runtime you would get with CR123 primaries while using those RCR123s from glowgadgets. The TK10 can technically run on a pair of 3.7V RCR123s and will have better runtime than any of the supposed "3.0V" rechargeable cells, but even better, would be a light that just runs on a single 18650, with double the watt-hour capacity of a pair of RCR123s, and about the same size. (the TK10 is not compatible with an 18650)
Don't fret, this will not be your last purchase, you are here now, the only hope is to lock away your wallet, burn your credit cards, (don't just cut em up, cuz you'll be piecing them back together to read the numbers for an internet order!)... There will almost certainly be more purchases in the future in the name of portable illumination. You will be absolutely blown away by the TK10 and really start to get interested at that point!
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Oh... BTW: the cells in that kit are 3.7V cells with voltage reducing diodes on the output, the charger is set to terminate the charge at around 4.4-4.5V to overcome the voltage shunting device in reverse, normal "3.7V" without that voltage regulating diode need to be terminated at 4.20V, so if you ever do buy any other lithium ion cells in the future that are "3.7V" type, do NOT charge them in the charger that came with your "3.0V" cells, they could explode.
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Eric
PS: to CPF: Please stop defaulting to the recommendation of CR123 powered fenix lights. It's not a productive recommendation considering that almost everyone who is recommended one here, goes looking for a rechargeable solution for it. Wolf-Eyes, DereeLight, LumaPower, JetBeam, Pila, Tiablo.... the list grows bigger all the time, we have plenty of options for 18650 powered lights, even Fenix jumped on the bandwagon with the TK11. You know how much it hurts having to tell someone "sorry, your rechargeable options all stink!"?