cyberindie, you ask a very good question! You have the world at your fingertips and I suggest you take advantage of it. There are many great resources for battery information, the site that Windstrings posted links to has a pretty good looking knowledge base where you can find FACTS about concepts such as capacities, applications, differences between battery types, different types of chargers, all kinds of interesting facts. Crate? What is Crate? I had no idea! Now I do!
Don't stop there, keep looking! Google!
How big is a C battery? How big are these "6000" batteries everyone's talking about?
How big is the battery compartment in your laser?
How big are the batteries that don't fit?
How big are the batteries that do?
What does Laserglow have to say? Ask them how much current your laser draws while you're chatting with them. Do lasers need a consistant current? Voltage?
Is there a difference between C cells and C size? (Ah Hah!)
Are there differences between rechargeable batteries and alkalines? OEM and OTC? What are they? Why are they important considerations?
How about rechargeable Lithiums?
Wait... oh yeah, How about e2 liths? I love e2's, does that mean that you should too?
Hey look at this! Did you know that the old-school NiCads still have certain advantages over NiMh batteries? Did you know that? Me neither, but I do now!
Listening to other people's experiences and opinions is great, but accessing information from the source(s) is not too bad either! I'll bet you're the scientifical type that is always curious and eager to learn. I hope this helps or at least amuses.
Oooooh, hey! Ohm's Law!