Karin stated the Raikage has Bijuu level chakra.
In the Madara vs Gokage fight Tsunade replenished the chakra of three Kages + she healed herself and used the chakra enchanted strength, but the Raikage run out of chakra before her.
While I would not say that the Raikage ran out of chakra before Tsunade, he definitely began to conserve chakra before Tsunade. Hinting that he too was low on chakra.
Which would suggest that Tsunade has chakra comparable to a bijuu. That said, she was seen doing more chakra heavy tasks than Raikage was. His chakra usage includes body flicker jutsu, ration armor, and ration hand. Whereas her chakra usage includes creation rebirth, healing and restoring the chakra of 3 kages, chakra enhanced strength, Byakugou for healing from yasaka magatama, healing from sussano swords, healing from Madara's powerful katon, and powering up Onoki's Jinton. Plus the mystery handseal.
So while A didn't run out before Tsunade did, he did begin to conserve his chakra, and we've yet to find anything that dictates Raiton Cloak uses a large chunk of chakra to maintain. Though I suppose it is conceivable. Though by the end of the fight, A had stopped using Raiton cloak, not only as made evident by chapter 591 but also by the fact that Madara managed to leave him such a state.