Solarforce L2P questions...

Gonna pick one of these up for my son to use (I'm sure we will share it...yeah right, we will be getting two) on our camping trips...my question is what drop in should I get for the thing...there are 14 million different ones and I'm not really up to speed on the difference from an XML to an XPG and so forth...the three mode will probably win out so I can put it on medium for when he is playing flashlight tag with others and we can switch to high to light up critters in the woods...

or is it cheaper to just buy the whole light...I think this would be the one for me...

http://www.solarforce-sales.com/product_detail.php?t=LF&s=45&id=305

anyone got a review that shows a 320 lumen compared to the 820 lumen...is this too much flashlight for a kid?...should I get him the 320 and me the 820?...possibly the one below for him instead?

I think I will go ahead and use the 18650 batteries that way we can have the same type while out and about in case we need to "borrow" a battery for one...is there an 18650 battery type (protected only ??) that you would recommend over others? anywhere local (like a Batteries Plus) going to carry these or are they an online type battery only?