Draining the battery on an ipad mini A1432

So i’m doing this iPad mini screen repair. I’ve used the CPB Heating mat to lose the adhesive tape so i can pry it open. The heating mat works wonders, it opens with less mess. I always test after opening the damaged screen to see if the iPad still works. The device works but since that screen is cracked really really bad, the touch screen doesn’t work at all. My question is, how long that the battery will last since I want that thing completely dies so i can safely disconnect and reconnect the ribbon cables. Please assist, thanks!