Proscenic D500 14.4V Replacement Battery 3400mAh

Proscenic D500 / D550 / GT320 — 14.4V Li-ion Replacement Battery (T-4S1P-B-U)

This 14.4V 3400mAh Li-ion battery pack fits the Proscenic D500, D550, and GT320 cordless stick vacuums. It replaces OEM part numbers T-4S1P-B-U, T-4S1P-B20, and YL18650-4S1P. Capacity is 48.96Wh — matched to the original specification.

• D500 / D550 / GT320 platform fit: All three models share the same 14.4V battery bay, connector pinout, and BMS handshake protocol. One cell pack covers the full range without modification.
• Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on the D500 motor platform. The BMS held overcurrent protection correctly under sustained suction load and returned accurate cell voltage to the indicator circuit.
• Dock charging practice for stick vacuums: Do not leave the vacuum sitting on the charging dock continuously between uses. Li-ion cells in stick vacuums experience accelerated capacity fade from trickle charge exposure. Charge to full, then remove the vacuum from the dock until the next use.

Suction dropping before the battery indicator reaches low

On the D500, the motor draws significantly more current when the filter is partially blocked or the brush roll is restricted. That elevated draw causes cell voltage to sag under load — the vacuum loses suction power while the indicator still shows a mid-range charge. The BMS reads resting voltage, not load voltage, so the indicator lags behind what the motor is actually experiencing. Clean the filter and check the brush roll before assuming the battery is at fault.

Motor cuts out briefly then recovers during a cleaning run

This is a BMS overcurrent trip, not a flat battery. When the D500 motor sustains a restricted airflow condition — blocked filter, sealed floor contact, or debris jam — current draw spikes past the BMS threshold and the pack disconnects to protect the cells. The BMS resets automatically after a few seconds, which is why the motor recovers without switching the unit off. Clearing the restriction is the fix. If it trips on a clean filter with no blockage, check that cell voltage under load stays above 12.0V — drop below that and the pack needs replacement.