End-of-life Battery Disposal Instruction:
This device uses a Lithium-ion battery that should last as long as the lifetime of the BW 900 system. If you suspect a defect of the battery then try to charge it. If the battery does not recharge, please contact your Sennheiser distributor for further repair information. 

If the battery appears to be dead and you do not want Sennheiser to replace it, you should follow the disposal instructions below. Please consult laws and regulations for proper battery disposal in your region. If there is no local regulation concerning battery disposal, please dispose it in a waste bin for electronic devices.

Caution:
The battery used in this device may present a risk of fire, explosion or chemical burn if mistreated. Do not expose batteries to heat above 100ºC (212ºF), or incinerate. Do not use or charge the battery if it appears to be leaking, discoloured, deformed, or in any way abnormal. Do not leave your batteries discharged or unused for extended periods of time. When batteries are misused, they may explode or leak, causing burns and personal injury. If your battery leaks, use normal precaution and discard it immediately.

Do not place in trash. Dispose the battery according to local battery recycling laws in your region.