Third Raikage vs Kabuto!

[LuckyMan]

Actually, Im not talking about that...
The thing that makes Kabuto's sage mode so good is not the snage sage mode per se, but the fact that with his experiments on his body he inplanted Juugo's cells upon himself. And with Juugo's cells he can absorb nature chakra passivelly...
Making his chakra essentially limitless.

No its not limitless. Juugo clan ability was to passively absorb nature energy, not chakra.

Nature energy is what is absorbed and after balancing it with your chakra you get senjutsu chakra. When SM users attack, they aren't attacking with just natural energy, thats impossible. The natural energy is combined with their own chakra and they are attacking that way so they're still losing chakra plus natural energy. As their chakra gets low, the amount of natural energy they can hold also gets lower, which lowers duration of SM, therefore when their own chakra supply runs out, so does their SM.