I'm pretty sure the QC35s still work fine as normal headphones with the battery dead and 3.5mm cable. That's how my Sony WH-1000XM3s work. You only need to turn

I'm pretty sure the QC35s still work fine as normal headphones with the battery dead and 3.5mm cable. That's how my Sony WH-1000XM3s work. You only need to turn them on to use noise canceling or have them be Bluetooth. They also quick charge giving a couple hours usage in a few minutes of usage. It's a bit of a tradeoff but the convenience is IMO worth it.