User blog comment:B214/Question & Answers 5/@comment-67.211.8.19-20150520130632/@comment-26209278-20150525194840

Don't think it'd be possible to do it, as he'd die from the stamina consumption.

But, let's say hypothetically, he could. His normal BG doubles his power every 10 seconds.

He can boost 6 times in a minute, 360 times in an hour. There are 8765.81 hours in a year(since there's 365 and a quarter days in a year). 8765 (rounded down, easier maths) times 360 is 3,155,400.

Issei could boost his power 3,155,400 (roughly) if he did not non stop.