I bought it about 18 months ago and at first it easily lasted 35 hours. Now it's gone totally downhill, even without ANC it doesn't last long. I tried resetting it and everything but nothing changes. Is it normal for the battery to degrade like that or is something wrong?
It's clearly battery degradation, it happens to all earbuds and headphones after some time, but 18 months is pretty fast to go from 35 hours down to 3-4 hours. Lithium-ion batteries wear down every time you charge them, so the more you use and recharge, the more they deteriorate. But what you're experiencing is really severe - you're losing like 90% of your battery life.
Before you give up, check a few things: try completely draining your headphones for a few hours, then charge them to 100% without interruption. That can sometimes reset the battery calibration. Also verify whether it's actually an ANC power drain issue or if it's across the board - malicious apps running or something constantly draining Bluetooth could be eating your battery. After you've done that, if it's still terrible, then the cell itself is dead.
Honestly, after 18 months with such a huge drop, you could contact Sony to see if they'll recognize this as a manufacturing defect (there's manufacturer warranty on the battery in a lot of regions). Otherwise you're stuck with either replacing the battery or buying a new one. It's frustrating but unfortunately it's something you can't really stop once the battery starts seriously wearing out.
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