Will device boot with no battery?

Hey, i was taking a look at a phone for someone who said it wont charge or turn on.

When plugged in a lighting bolt in a circle appears but no battery percentage. i took apart the phone and disconnected the battery then plugged in the charger and same thing

Lighting bolt in a circle with no battery percentage

Does this mean the battery is the problem? The device in theory should boot without one while plugged in like a laptop.

Would this mean the issue is software and not hardware since the charging port is working.