Underneath the clean Android One skin lies the heartbeat of MediaTek. The firmware contains the proprietary "MTK" binaries. These are the drivers that control the radio, the aging camera sensor, and the battery management.
In cases where the phone is "bricked" (unresponsive) or stuck in a boot loop, the firmware must be manually reinstalled. Since the Blade L220 uses a Unisoc chipset, this process usually involves using a PC and the SPD Flash Tool Firmware ZTE Blade L220