Is my battery in my iPhone faulty, or something more? I have an iPhone 7. I had the battery replaced approx 6 months ago.

I've noticed the battery life hasn't been overly great considering it's a new battery.

Yesterday, my phone started turning off at random. Today, it turned off and never turned back on.

When the phone is plugged into the AC charger, it gets stuck in a boot loop on the Apple logo. But, when it isn't plugged in, I get no power.

I've taken the battery out, and the exact same thing happens. It boots to a boot loop on AC power, and no power when unplugged, as expected. It's as if it won't run off its own battery source.

Does this sound like a faulty battery or something more significant like the IC board?

I cannot boot into restore mode or off a USB port.
My experience is you can triage it with these steps:


Have you tried to do the force restart command while it is plugged into ACC even if your phone has no power?
Have you tried using a different charger or socket? 
Have you noticed any pattern in what the charge remaining is when the shut downs happen? (If they are spread equally - less likely the battery, if they cluster around certain voltage levels - likely the battery)


Also, my tactics would be to wait about half an hour after plugging your phone in just to see if anything happens.  My old iPhone 5 was useless for half an hour after I plugged it in when it was completely flat since it took a very long time to get past the weak area with lower voltage but worked OK at the top end.

Your symptoms could be logic board, but are much more likely a battery causing it instead of a short or electrical failure.