AirPods Max won’t power on or charge

Hi everyone,
I bought a faulty pair of AirPods Max to try repairing them myself.

Originally, the charging power kept dropping over time (about 3W → 2W → 1W → 0W) until it eventually stopped drawing any power at all. When I connected a charger and pressed the button, the LED would blink amber, and then it started blinking green. Even with the charger connected, the headphones wouldn’t function, and repeating the reset procedure didn’t help. If I unplugged the cable, there was no response at all, so I assumed the battery was completely drained and replaced the battery.

After replacing the battery, the only change is that the LED behavior went from blinking green to blinking amber—but nothing else improved. It still shows 0W draw even with the charger connected, and it won’t charge or power on.

In a case like this, what would you suspect as the likely cause? What parts or components would you recommend checking or replacing next, and what troubleshooting steps should I try?

Thanks in advance!