Siemens Rexton WL200AP Remote Control Replacement Battery 3.7V 850mAh

Siemens Rexton WL200AP — 3.7V Li-ion Replacement Battery (21221-10296051)

This is a 3.7V 850mAh Li-ion battery for the Siemens Rexton and WL200AP hearing aid remote control. The remote lets users adjust volume and switch hearing aid programs without touching the devices directly. When this battery depletes, that wireless control is gone — this replacement restores it.

• Rexton and WL200AP remote fit: Both the Rexton and WL200AP remote controls share OEM part number 21221-10296051, the same 3.7V cell architecture, and the same connector footprint — one battery covers both units without modification.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on the bench. The protection circuit tripped correctly at low-voltage cutoff and accepted a clean full charge without thermal anomalies.
• Single-cell remote replacement tip: This remote runs on one cell, so there is no pairing concern — but before reinstalling the cover, confirm the polarity markers on the battery align with the markings inside the battery bay. Li-ion cells installed backwards will not charge and may trigger the protection circuit immediately.

Why the Rexton remote stops responding before the battery is fully flat

The IR LED in this remote requires a minimum voltage to fire a signal strong enough for the hearing aid to detect. As the Li-ion cell ages and internal resistance climbs, voltage sags under the brief current draw of each button press — even if the resting voltage looks acceptable on a meter. The remote appears dead but the cell is not truly empty. Replacing the cell at this point, rather than waiting for complete failure, is the correct call.

Remote works after install but range drops to a few centimetres

Short range after a new battery install usually means the cell seated but is not making firm contact with one terminal. A loose connection limits current to the IR LED, reducing output power without killing the remote entirely. Remove the battery, check for debris or corrosion on the contact pads, reseat the cell firmly, and confirm the cover clicks fully closed. The remote should respond reliably at normal arm's-length distance — roughly 0.5 to 1 metre — once contact is solid.