No connection between battery and motherboard

Hi!

The battery terminals (BT+ and BT-) on the left speaker read 3.45V, while on the right (B+ and B- I assume?) I get... 0.04V. When a charger is connected the right reads 4V, while the left, well, still 3.45. The red charging light is blinking, the headphones don't boot from the battery (duh).

I assume the connection is broken somewhere in the headband or the hinges, how could I disassemble those? (Is it even possible?)