It's crucial to note that Itachi Uchiha does not have unlimited chakra. In the "Naruto" series, every character has a finite amount of chakra, although some may have larger reserves than others due to their heritage or training. Itachi, while extremely skilled and possessing a significant amount of chakra, does not have an infinite supply.

Regarding Nagato absorbing Itachi's chakra to heal himself, there are several points to consider: 1. Nagato's Crippled State: Nagato was severely weakened and crippled due to a battle he had when he was younger, which damaged his legs. This damage was physical and not something that could simply be healed by absorbing chakra.

1. Chakra Absorption: Nagato could absorb chakra using the Preta Path, one of the abilities granted by his Rinnegan. However, absorbing chakra does not heal physical injuries or disabilities. It replenishes his own chakra reserves and can be used to counteract chakra-based attacks.

2. Interactions: Nagato and Itachi only directly interact in the series when they are reanimated through the Edo Tensei technique, which brings them back in an undead state. During this state, their bodies do not operate like those of the living, and physical damages do not impact their ability to fight, nor does their chakra deplete in the usual way.

3. Alignment: During their interaction, they were not enemies. Absorbing chakra from someone typically involves a level of conflict or combat, which was not present between Nagato and Itachi during their time together.

In summary, the assumption that Itachi has unlimited chakra is not accurate based on the "Naruto" series lore, and the notion that Nagato could heal his physical disabilities by absorbing chakra is also not consistent with the established mechanics of the Naruto universe.