That an interesting choice, I like it. I know 100mW 532nm modules can be run for under a min without a heat sink. Although I'm not completely sure about infrared I'd say you can get away without a heat sink for short run times.
That being said I'd recommend using a heat sink and I think most here would aswell.
I wouldn't suggest hooking it up straight to batteries. The voltage might be correct and it may work but since diodes are current hungry devices. They will attempt to take as much current as they can from the batteries and though it MAY work. There's no telling how long it WILL work for. So just be aware that not having a heataink and driver is not a good idea and is suggested if you would like your diode to live for more than a few minutes.
Then you should be fine. I didnt click the link. I just read the thread title pps: A 100mw doesn't produce a lot of heat but I would advise paying attention to how warm the module gets. For general pointing you shouldn't need a heat sink but if you plan to use it in some sort of application where the laser needs to be on for more than a minute or two I would find a way to heat sink it.