I have to admit that I am surprised to see how many here use LI batteries rather than the far more economical option of using Eneloops.
Maybe I took the title of the forum too literally; or maybe the budget-oriented mindset applies mostly to the flashlights, and not so much to other facets of the hobby?
For what it's worth I couldn't care less what types of batteries people use. I guess I just expected to see a heavy bias toward NiMH, and this thread is just me expressing my surprise to see so much discussion of LI lights.
If i did not try a li-ion scavenged from a dead laptop battery and tried it in a romisen RC-C8 i would probably be still in the dark about li-ion. Fortunately i did. Li-ion and similar's (IMR, li-po) are the king of batteries each for its own job.
AA's ni-mh are still prety decent when you need a cereless solution to power some lights.
Each battery type has its own advantages and disadvantages.
NiMH are safe and cheap. LSD NiMH also hold their charge fairly well in normal circumstances (i.e. at home, not in the car during hot summer days).
Li-ions are more expensive if you want good quality cells, and are more dangerous than NiMH (especially in extreme conditions, but you also need to check their voltage regularly, not to overcharge or over discharge them [and hope the protection circuit doesn't fail], carefully match voltage when using multiple-cell configurations, etc.).
Primary lithiums are expensive but are the best for emergency situations (very long shelf life, durable and usable under extreme temperatures) or for low discharge devices (such as remote controls, alarm clocks, etc.).
Since most people here look for the most juice in the smallest package, and know about the dangers of li-ions and how to avoid them, li-ion is the most discussed type of batteries here.
For me, that right there is reason enough to stay away from LI. With NiMH everything feels practically fool-proof, and that's a huge advantage for someone like myself.
Additionally, I'm not preoccupied with the lumens "arms race", so getting insane output isn't a huge priority here. If I'm going to be honest then I'd say that the most I ever really need is something like 40-50 lumens; the rest is just for fun.
Well you can run pretty decently an XM-L to close full power with 4AA eneloops (or similar good mi-mh's) anyway. No need to be in the "dark" with Ni-mh's. Afterall there is plenty of 3xD size ni-mh XM-L mag mods aroud working rather nicely. Li-ions are dandy since they are small for capacity and very low self discharge. If ni-mh were close to the level of li-ion nobody would ever use them.
Most budget offerings use lithium batteries, so in order to get a decent selection, you kinda need the batteries.
Plus, once you've forked over for the inital investment, you can use them for years and use the chargers indefinitely.
I do agree that getting a smart universal charger and some eneloops is a far better plan since you can use those batteries around the house. However, most of the flashlights in certain categories that use them are expensive.
Say you want a big light. Fenix TK70 is the only 4xD one I can think of with 2000+ lumens. All budget ones are multiple 18650s. For a solid 2C sized light, those don't exist. A Fenix TK41 or itp A6 Polestar use 6 or 8 AA batteries in a carrier. If you want a truly bright keychain or easily pocketable light, a CR123 or 14500 is the clear winner.
You CAN get inexpensive romisens that use 3xAAAs for flood to throw which is nice.
You CAN get 2xAA general purpose lights which are solid.
But for small or large lights, lithium is almost a requirement (unless you pay big bucks)
You have to measure under load not open circuit voltage ... Eneloops are 1.2 and LiIon 3.7 ... fresh of the charger Eneloops are up to 1.51 V and LiIon 4.2, but that's not their rated voltage.
I resisted the LiIon train for a long time and I only own 4 high quality 18650 cells (2 Himax 2400 and 2 XTARs 2600), the energy density of the 18650 is just something else. As long as one sticks to protected high quality cells and a good charger and single cell setups... there is really no reason to avoid them. Every Notebook uses them.