But as I said, if chakra could be put into points, Preta Path would logically cost as close to 0 chakra as possible, due to the fact that it works mainly to absorb chakra, so if it cost a large or even moderate amount of chakra, there would be no point in using it. Also, it is their choice to change how they use their chakra, just because their low doesn't mean they are forced to use less chakra, they could put the last of it into their technique to try and take the enemy down with them. So no, Sage Mode Naruto would not have unlimited chakra, that logic doesn't even make sense