About this replacement
Worx WX373 Brushless Impact 20V MAX Drill — 16V Li-ion 5000mAh Replacement Battery (WA3527)
This is a 16V Li-ion battery rated at 5000mAh (80Wh), built to replace the WA3527 and WA3539 packs used in the Worx WX373 Brushless Impact 20V MAX Drill and compatible WX152 platform tools. It slots into the same battery bay and connects via the standard Worx 20V slide-rail interface. Capacity is sourced from the product specification — not estimated from third-party data.
- WX373 and WX152 platform compatibility: These models share the same 16V nominal slide-rail connector and BMS communication protocol. The battery management system uses the same cell-count configuration and voltage curve, so the charger handshake completes without modification or adapter.
- Bench tested on actual hardware: We ran this pack through motor-start inrush cycles on the WX373 trigger at full torque setting. The BMS held without tripping overcurrent protection, and cell balancing kicked in correctly at the top of each charge cycle.
- First-use torque ramp on WX373: Run the drill at half-load torque for the first two charge cycles before driving into hard materials at maximum setting. This lets the BMS log the motor's inrush current signature and set accurate overcurrent thresholds before you put full load through the drivetrain.
BMS cutoff on WX373 motor-start inrush surge
When you pull the WX373 trigger at full torque from a dead stop, the brushless motor draws a short inrush spike that can be three to five times the steady-state current. A new or recently stored pack may not have a calibrated inrush profile in its BMS, so the protection circuit reads the spike as a fault and cuts the output rail. This is not a defective battery — it is the BMS acting conservatively before it has logged real motor behaviour. Two or three partial-load cycles re-calibrate the threshold and the cutout stops occurring.
Charger blinking red on a new WA3527 pack after storage
Li-ion cells that have sat in a warehouse drop below the charger's minimum acceptance voltage — typically around 2.5V per cell. The Worx charger reads the pack voltage on insertion, and if any cell group sits below that floor, the charger signals a fault with a red blink rather than beginning a charge cycle. Place the pack in the charger, wait 60 seconds, then remove and re-insert — some chargers will attempt a low-current recovery pulse on the second insertion. If the red blink persists after three attempts, check that each cell group reads at least 2.5V before concluding the pack is unrecoverable.