Plantronics Poly SY20 USB-A Compatible Battery 3.7V 3350mAh

Plantronics Poly SY20 USB-A — 3.7V Li-ion Replacement Battery

This 3.7V, 3350mAh (12.4Wh) Li-ion cell replaces the internal battery in the Poly SY20 USB-A portable conference speakerphone. It fits the SY20 directly and restores audio output capacity when the original cell has degraded from regular use or age. No OEM part number is published for this cell — match by model before ordering.

• Poly SY20 USB-A platform fit: The SY20 runs a single-cell 3.7V Li-ion pack powering both the speaker amplifier and the USB-A communication stack. This replacement cell matches that voltage rail and physical footprint, so the BMS on the SY20 board reads state-of-charge correctly without recalibration.
• Bench tested on actual hardware: We cycled this cell through the SY20's charge circuit and monitored BMS handshake under combined amplifier and USB load. The cell accepted a full charge cycle, held voltage above the BMS low-cutoff threshold, and the unit reported charge status accurately throughout.
• Fuel gauge reset after swap: After fitting a new cell, run the SY20 down to the low-battery indicator before the first full recharge. The SY20's fuel gauge anchors its empty reference on the first discharge — skipping this step causes the indicator to read inaccurate charge levels from day one.

Capacity fade from constant desk-top charging on the SY20

The SY20 lives on most desks plugged into USB-A constantly, which means the cell rarely drops below 80% before the charge circuit tops it off again. Shallow cycling like this compresses the Li-ion charge window over time — the cell stops using its full capacity and the fuel gauge starts reporting full when it isn't. Once this pattern is established, swapping to a fresh cell only helps if the charging habit changes. Discharge the SY20 below 20% at least once a month before reconnecting USB to keep the cell cycling across its full voltage range.

Audio distorting before the battery indicator reaches empty

This happens when the Li-ion cell can no longer hold voltage under the amplifier's current draw — the cell voltage sags below the amplifier's clean operating threshold before the BMS trips the low-battery warning. The result is amplifier clipping: audio breaks up or distorts while the indicator still shows charge remaining. It is not a speaker fault. A degraded cell with reduced internal capacity sags harder under load than a fresh cell at the same state-of-charge. Fitting a new cell restores the voltage headroom the amplifier needs — verify this by checking the SY20 reads at least 3.5V under load during playback.