Newb question on Input numbers for P60 modules

I am loking to upgrade a few of my older P60 module SF's (G2 & 6P Defender) and am having trouble understanding input value's.

Full disclosure: I have a boatload of SF CR123's as well as UltraFire 3.6V rechargables.

The Module's that im looking to upgrade to list a "minimum" input of 3.7V

http://www.dealextreme.com/details.dx/sku.11621

http://www.dealextreme.com/details.dx/sku.11836

Is that a "suggested" input level for optimal performance to reach that maximum lumen's level or an absolute minimum (like the light would not work if I attempted to run it with the batteries that I have available on hand?)

I know it might be a rookie question but its been on my mind all day and I cant seem to get any concrete info on it one way or another.

Also, would my recharger (for 3.6v) work if I were to buy 3.7v rechargables for it?

Thanks guys lovecpf

Hey man, welcome.

The figure listed is where the regulation runs. It will usually remain a constant brightness in that voltage range.
Once it drops below that it will run at "direct drive".

If your rechargeables are protected they will run until this protection kicks in and if your batteries are unprotected they will drain down all the way and even harm them.

Those 3.6v cells are really 4.2v when fully charged so your charger and cells are the right ones.

You usually get longer runtime with the 18650 rechargables as the output drops once out of regulation. ie, less light out but more runtime.

3.6V = 3.7V = 4.2V cells

BUT.. there is an exception to the 3V rechargeable cells.. they're 3.6V w/o load.. though they are rarely listed as that.

You guys are the best. Thanks!

So I should be good to go with the R2 single mode module(linked above) in combination with the batteries that I already have on hand?

All of my RCR123 3.6v are "protected" BTW.

So if I'm understanding what you guys said correctly: when the 123's begin to lose juice, the brightness of the light will remain about the same and then the light would suddenly "die"?

With the 18650's, as the juice runs out, the light will decrease in brightness but remain useable?

2x RCR123 with protection cutting in at say 2.7v will leave you running in regulation till switch off (5.4v) but the 18650 will drop out of regulation and then run for a while getting dimmer and dimmer till cutoff.