NARWAL DH2104CYJ 21.6V Replacement Battery BP-6S1P

NARWAL DH2104CYJ / S1 Max — 21.6V Li-ion Replacement Battery (BP-6S1P-3600A)

This is a 21.6V 4000mAh (86.4Wh) Li-ion replacement battery for the NARWAL DH2104CYJ and S1 Max robotic vacuum cleaners. It slots into the same bay as the original and powers the suction motor, navigation sensors, and onboard electronics. Capacity figure is taken directly from product specifications — 4000mAh at 21.6V nominal.

• DH2104CYJ and S1 Max compatibility: Both models run the same 21.6V six-cell series pack with identical connector pinout and BMS communication protocol. A single cell configuration — BP-6S1P-3600A or BP-6S1P-3600D — covers both. No wiring adapters or firmware changes needed.
• Bench tested on actual hardware: We cycled this pack through discharge under simulated suction load. The BMS held cell balancing across all six series cells and triggered over-discharge protection cleanly at the correct cutoff threshold — no premature shutdowns and no cell voltage divergence after ten cycles.
• Dock charging behaviour on the DH2104CYJ: Do not leave the vacuum sitting on the charging dock continuously. NARWAL robotic vacuums on permanent dock connection develop capacity fade significantly faster than units charged only when depleted. Charge to full, then remove from the dock until the next cleaning run.

Cordless vacuum losing suction before the battery indicator reaches low

This happens when the suction motor is working harder than normal — usually because of a restricted filter or partial blockage — and draws more current than the BMS allows under sustained load. The BMS reads cell voltage sag under that elevated current draw and throttles output before the state-of-charge indicator has time to catch up. The indicator is calculated from a resting voltage model, not real-time load current, so it lags behind actual capacity under stress. Clean or replace the filter first; if suction recovers, the battery was not the root cause.

Motor cuts out mid-run then recovers after a few seconds

This is a BMS overcurrent trip, not a dead battery. When airflow is restricted — blocked brush roll, clogged filter, or sealed intake — the motor draws a sustained current spike that exceeds the pack's continuous discharge rating. The BMS opens the output FET to protect the cells, the vacuum stops, and after a brief thermal or timer reset window the BMS re-closes and the unit starts again. Clear the blockage, check that the filter is seated correctly, then restart. If the cutout continues on a clear, unblocked vacuum, check that pack voltage at rest is above 20V before ruling out a failing cell.