Braun 3722 Replacement Battery 3.7V 650mAh Li-ion

Braun 3722 / 3723 Series — 3.7V Li-ion Replacement Battery

This 3.7V 650mAh Li-ion cell replaces the internal battery in Braun electric shavers across the 3722 and 3723 lineup, including variants 3722 S26.523.3 and 3722 S26.500. It fits the compact cell bay used across these foil shavers and matches the original voltage and BMS handshake requirements. Swap it when the original cell no longer holds a charge or the shaver cuts out before the low-battery indicator triggers.

• 3722 and 3723 compatibility: These models share the same internal cell format, voltage rail, and connector orientation. The BMS in each variant expects a 3.7V nominal cell — using the wrong voltage causes an immediate protection trip on first charge.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a 3722 body. The BMS accepted the cell without fault codes, charge current stepped down correctly at 4.2V, and the protection circuit tripped cleanly at the low-voltage threshold rather than allowing deep discharge.
• Port drying before charging: For any wet shave use, dry the charging port completely before connecting the charger. Moisture bridging the charging contacts triggers a BMS protection fault that the shaver reports as a dead battery — not a charging error — sending users down the wrong fault path.

Capacity fade from daily partial charging on the 3722

Most 3722 users charge the shaver every morning after a short shave, topping up from 60–80% rather than depleting the cell. Li-ion cells cycled repeatedly in the upper voltage band develop a narrower usable capacity window over time. The fuel gauge drifts because the shaver's charge counter was calibrated against a full cell, not a partially aged one. Running the cell down fully once every few weeks lets the BMS recalibrate against the actual capacity and slows indicator drift.

Shaver motor speed drops before the low-battery indicator activates

This happens when the cell's internal resistance has risen enough that motor start-up current causes a voltage sag below the motor's minimum operating threshold — but not low enough to trigger the BMS cutoff. The indicator reads the resting voltage, not the loaded voltage, so it still shows charge remaining. A cell with high internal resistance will sag hard under the brief current spike when the motor starts. Measure resting voltage: if it reads above 3.5V but the motor still bogs, the cell needs replacement.