Siemens VK40B01/03 Cordless Vacuum Compatible Battery 9.6V 1800mAh

Siemens VK40B01/03 — 9.6V Ni-MH Replacement Battery (91702901)

This is a 9.6V, 1800mAh Ni-MH replacement battery for the Siemens VK40B01/03 and VXAS020V09 cordless vacuum cleaners. It replaces OEM part number 91702901. The battery slots into the same bay as the original and uses the same connector configuration.

• VK40B01/03 and VXAS020V09 compatibility: Both models run the same 9.6V Ni-MH cell arrangement with matching physical dimensions and connector polarity. The BMS on each accepts the same charge termination signal, so the same replacement cell works across both platforms without modification.
• Bench tested on actual hardware: We ran this battery through charge and discharge cycles on a VK40B01 unit. The BMS accepted charge termination cleanly, motor spin-up reached rated speed without voltage sag, and the cell temperature remained within spec across sustained operation.
• Dock charging discipline for Ni-MH cells: Do not leave this vacuum sitting on the charging dock between uses. Ni-MH cells degrade faster under continuous trickle charge than from regular discharge cycles. Charge fully, then remove from the dock and store the vacuum off the charger until the next use.

Suction dropping before the battery indicator reaches low

On the VK40B01/03, suction loss often happens while the battery still shows charge. The motor draws more current when airflow is restricted — a partially blocked filter or full dust cup increases the load and causes voltage to sag under draw. The BMS reads this sag as a low-cell condition and reduces power to the motor before the indicator reflects it. Clear the filter and empty the cup before assuming the battery is at fault.

Motor cuts out mid-clean and then recovers after a short pause

This is a BMS overcurrent trip, not a dead battery. When suction is restricted — blocked nozzle, clogged filter, or a sustained seal against carpet — the motor draws current above the BMS threshold and the pack shuts down briefly to protect the cells. After a few seconds the BMS resets and the motor restarts. Clear the obstruction, check the filter, then restart the vacuum. If the cut-out repeats on a clear filter, check cell voltage under load — a degraded pack will sag below 8.5V and trip the overcurrent threshold without an actual blockage present.