About this replacement
Electrolux ERG36 / WQ61 Series — 18.5V Li-ion Replacement Battery (BABP185LI20-TP)
This 18.5V 2500mAh lithium-ion battery replaces the original pack in the Electrolux ERG36 and WQ61-series cordless vacuums. It fits directly into the battery slot and connects via the same multi-pin interface as the factory unit. Voltage and capacity match OEM spec: 18.5V, 2500mAh (46.25Wh).
- ERG36 and WQ61-series fit: These models share the same 18.5V battery rail, connector pinout, and BMS communication protocol. One battery pack covers the full range — ERG36, WQ61-42GG, WQ61-44SW, WQ61-46DB, and the remaining variants in the series.
- Bench tested on actual hardware: We ran this pack through full charge and discharge cycles on the ERG36 platform. The BMS handshake cleared without fault codes, charge acceptance was normal, and the motor controller received clean voltage through the discharge curve.
- Dock charging behaviour on the WQ61 and ERG36: Do not leave the vacuum sitting on the charging dock permanently. These units trickle-charge when docked and the pack stays at capacity. Continuous trickle charge accelerates lithium cell degradation. Charge to full, then remove from the dock.
Suction dropping before the battery indicator reaches low
The ERG36 motor draws significantly more current when the filter is partially blocked — the motor works harder to maintain airflow, pulling the battery voltage down faster than normal. The battery indicator reads cell voltage, not remaining capacity, so a loaded motor can drag voltage low while the indicator still shows mid-range. Clean or replace the filter first. If suction recovers immediately after filter cleaning, the battery is not the cause. If suction remains weak with a clean filter, the pack is likely capacity-faded and holding voltage poorly under load.
Motor cuts out and then recovers after a few seconds
This is a BMS overcurrent trip, not a motor fault. When sustained suction restriction forces the motor to draw beyond the pack's overcurrent threshold, the BMS opens the discharge circuit to protect the cells. The pack resets after a short cooldown — typically a few seconds — and the motor restarts. Check the filter and brush roll for blockages before assuming the battery is faulty. If the cutout happens on a clean filter with no blockage, measure resting pack voltage — a healthy 18.5V cell group reads above 20V off the charger.