Worx WA3503 12V Replacement Battery 1500mAh Li-ion

Worx WX125.3 Series — 12V Li-ion Replacement Battery (WA3503)

This is a 12V 1500mAh Li-ion battery that fits the Worx WX125.3, WX125.3 D-Lite, WU288, and WX125 series compact cordless tools. It replaces OEM part numbers WA3503, WA3509, and WA3505. Capacity is 18Wh — identical to the original specification.

• WX125 platform compatibility: The WX125 series shares a common 12V slide-pack connector and BMS handshake across the drill, impact driver, and reciprocating saw variants. The battery rail contacts and cell configuration match the original pack geometry, so no adapter or modification is needed.
• Bench tested on actual hardware: We cycled this pack on a WX125.3 drill through repeated load sequences. The BMS held the overcurrent threshold correctly during motor-start inrush and cut off cleanly at low cell voltage without false trips under sustained trigger pulls.
• First-use load conditioning: Run the tool at half load for two cycles before full-torque applications. This gives the BMS time to profile the motor's inrush current draw and set its overcurrent protection thresholds accurately before you push the tool hard.

BMS cutoff on motor-start inrush in the WX125 drill and reciprocating saw

The WX125 reciprocating saw draws a sharp current spike the instant the trigger is pulled — this inrush can be three to five times the steady running current. A BMS that hasn't profiled the motor yet may read that spike as a fault and trip the overcurrent protection. The result looks like the tool cutting out immediately on trigger pull, then recovering after a second. Running two half-load cycles first lets the BMS log the inrush signature and distinguish it from a genuine short-circuit event.

Tool bogs under load or loses torque mid-cut

Voltage sag under heavy load is the most common cause of a WX125 tool feeling weak or slowing mid-cut. At 12V and 1500mAh, the cell headroom is limited — if the rail contacts on either the tool or the battery pack have oxidation or debris, resistance at the contact point amplifies sag significantly. Clean the slide-pack contacts with a dry cloth and check that the pack seats fully until the latch clicks. If the tool still bogs, measure pack voltage under load — it should hold above 10.8V during a sustained cut.