Random reboots; won't power on; weird screen colors

My 8 Plus frequently and randomly powers off and/or reboots. Sometimes during use and sometimes when it’s just sitting there untouched. Sometimes it will power off for hours on-end even when connected to power. When it reboots, it will typically go through multiple reboot cycles. During these cycles, the screen sometimes shows random solid colors (red and green) or a pixelated “rainbow” screen.

Should I attempt a battery replacement or chalk it up as a motherboard issue and buy a new phone? I’ve attempted hard resets, DFU restore, reformatting, etc. to no avail.