@Thex ... actually, the size (dimensions) & rated capacity/runtime of a cell is the main way to determine how long it will last. I'll extrapolate in a moment, but first...
There ARE some advantages to Li-Ion over even Ni-Mh (Nickel Metal Hydride) and some other battery solutions simply because of what is called "energy density". It's basically a way to say "pound for pound or ounce for ounce--THIS battery technology has more power than THAT battery technology".
In the case of Li-Ion cells... most research & spec sheets show that they are superior to most (read: MOST) battery chemistries available on the consumer-level market today. Additionally, Lithium is the lightest metal on the periodic table... and thus, these cell types tend to weigh less when compared to an equally-dimensioned/sized cell of a different chemistry (for example, Alkaline).
Now... to go back to my earlier point about which tends to last longer. Direct current... is direct current. Whether from Lead-Acid (car batteries), Ni-Mh, Ni-Cad, Alkaline or otherwise. And capacity--to some extent--is capacity. If a battery company isn't "cheating their specs"... if for example:
a Li-ion cell is rated at "2200mAh"... and...
a Ni-Mh cell is rated at "2200mAh"... then...
...they should last nearly the exact same time, if placed under precisely the same conditions. In this case, if you drew 1A (1000mA) consistently from these cells, they will be exhausted of their current charge in approximately 2.2 hours. By the way people... try NOT TO CONFUSE "mAh" with "mA". One is drawing current OVER TIME (like miles per hour). The other is just plain current.
BUT... and there is always a but... there are also OTHER things to be considered... such as DISCHARGE CURVES.
Oh great. Nova's talking MORE gobbeldy-gook. But really... if you learn about it... you'll understand why Li-Ion is currently THE best solution for things such as LED sabers.
To sum it all up... you have *ALL* noticed the sort of "slump" alkaline cells can have. In all SORTS of devices--let alone your saber. You know what I mean... the "dimming" that begins to occur (or even color shift if you have an RGB setup) with alkalines or even Ni-Mh cells. It's irritating, because it's like... you know... the cells die before they
REALLY die, right? Precisely.
Well, Li-Ion cells have an extremely "FLAT" discharge curve. In other words--they do not really sacrifice voltage to maintain current output during their discharge cycle. What the bloody blazes am I blithering about. IT TRANSLATES TO: You Get An Even Brightness and/or Color With Your Saber From Full Charge To The "Time to Recharge" Point. Got it?
So... I know I took a VERY long and circuitous route to answer the question, but... it would behoove some of the forum members to look up a little information on battery cells, battery chemistries... and you'd be surprised at the info you'll find.
To REALLY REALLY SUM UP:
* I've been using Li-Ion cells in sabers since 2005/2006.
* I have probably used more sabers more often than most of the people here combined
* I've spent almost NO money on battery replacements over the past 5 years... and that is more awesome than I could have EVER imagined
* They are lighter, "smarter", more energy-dense and powerful (3.7v vs. 1.2v or 1.5v) than anything else I've encountered... and at reasonable cost
Soooo... why WOULDN'T you use them?