last 3 percent of battery is saved on purpose for booting up the phone. It is made to work like that. If you use all the battery juice It will not start up. mark this as solution by pressing 3 dots. since your phone is new you need to calibrate your battery 🔋 too. Charge fully then use the battery till your phone goes off. Then charge again till 100 percent without using your phone. You will see some difference. Good luck
