The rail has exposed contacts along it's length, so if you have the correct optic/PEQ box which can accept power input by that method instead of internal batteries, the idea is you can run everything via AA/AAA/CR123s loaded in to the quick-change pack near the magazine. Imagine tactical scalextric, and you're not too far off.
RESET make the real RIPR, far as I know though, it's not taken off in the real world on account of the fact it makes your rifle unwieldy and even heavier than it already is. Also a lack of companies making specific versions of their accessories to integrate with the system is sort of a killer. Considering how many 1000s of hours the batteries can last in RS red-dot optics I don't see the appeal myself, carry a spare set of cells for your light and laser designator and you're sorted without the extra bulk, weight and cost.
Edit: Also I'm pretty sure the power packs are shaped like a real magazine, so you can use it the same way as you would a RediMag/RediMod and just store extra ammo up there.
