he used sage mode many times which is said to replenish his chakra. most of the chakra naruto is using is kyuubi not his own except when he counter madara's moktun and when he fight kyuubi.how long has he been fighting in the war? how much chakra has he used?
yet he can split his chakra this many times to create clones to get out of the son goku stomach
You must be registered for see links
he has more chakra then nagato in base