Worx WA3593 20V Replacement Battery 4000mAh Li-ion

Worx WU380 / WU388 Series — 20V Li-ion Replacement Battery (WA3593)

This 20V Li-ion battery replaces the Worx WA3593, WA3595, WA3596, and WA3401 packs. It fits the WU380, WU388, WU185, and WU294 cordless multi-tools and related handheld power devices. Capacity is 4000mAh (80Wh) — matching the original cell specification.

• WU380 and WU388 platform fit: These models share the same 20V slide-rail connector, BMS handshake protocol, and cell voltage window. One battery pack covers both tools without any modification or adapter.
• Bench tested on actual hardware: We cycled this pack through repeated motor-start inrush events on the WU380 platform. The BMS held the overcurrent threshold without tripping under standard accessory load, and cell balancing completed correctly after each charge cycle.
• Break-in load management: On first use, run the tool at half load for two cycles before applying maximum torque or sustained cutting pressure. This lets the BMS profile the motor's inrush current draw and set accurate overcurrent protection thresholds before heavy use begins.

BMS cutoff on motor-start inrush during accessory changes

The WU380 draws a sharp current spike the instant the motor starts — this is inrush current, and it peaks well above steady-state draw. On a new or freshly stored pack, the BMS overcurrent threshold may not yet be calibrated to the motor's signature, causing it to trip and cut power immediately on trigger pull. Running two break-in cycles at moderate load trains the BMS to distinguish inrush from a genuine fault. After that, the tool starts cleanly across all accessory types.

Charger shows blinking red on a new pack pulled from storage

Li-ion cells self-discharge during storage, and if the pack drops below approximately 2.5V per cell, most chargers will refuse to begin a charge cycle — the blinking red LED is the charger's low-voltage rejection signal, not a sign of a dead battery. Some Worx chargers include a recovery mode: leave the pack seated for 10–15 minutes and the charger will attempt a trickle pre-charge to bring cells back above the acceptance threshold. If the charger does not recover automatically, confirm the pack reads at least 12V total across the terminals before concluding the cells are at fault.