Worx WA3540 12V Replacement Battery 5000mAh Li-ion
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Worx WA3540 12V Replacement Battery 5000mAh Li-ion - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
Battery Care Tips
🔹 Getting Started
Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.
🔹 Keep It Healthy
Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.
Delivery and Shipping
Delivery and Shipping
🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.
Disclaimer
Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
Worx WA3540 12V Replacement Battery 5000mAh Li-ion - is backordered and will ship as soon as it is back in stock.
Voltage
12V
Amp
5000mAh
Worx WU137 / WU161 — 12V Li-ion Replacement Battery (WA3540)
This is a 12V 5000mAh Li-ion replacement for the Worx WA3540 battery pack. It fits the WU137 and WU161 cordless tool platforms — drills, impact drivers, and compact saws that share the same 12V slide-in battery interface. Voltage and capacity match the original pack exactly.
- WU137 and WU161 platform compatibility: Both models run the same 12V rail and use an identical battery slot with the same connector pinout and BMS communication handshake. One pack works across both tools without modification.
- Bench tested on actual hardware: We ran this pack through charge cycles on a WU161 platform and monitored BMS response during motor-start inrush. The protection circuit handled repeated trigger-pull spikes without nuisance tripping at rated load.
- Break-in load cycling: On first use, run the tool at half load for two cycles before applying maximum torque. This lets the BMS log the motor's inrush current signature and calibrate overcurrent thresholds before you push the tool hard.
BMS cutoff on motor-start inrush surge with the WU137 drill
When you pull the trigger on a stalled or high-resistance load, current spikes sharply in the first 20–50 milliseconds before the motor reaches speed. On a 12V pack, that inrush can briefly exceed the BMS overcurrent threshold, tripping the protection circuit before the motor has even turned. This is more common with worn tool internals or a dull bit increasing stall torque. If the pack shuts off on trigger pull, release the trigger, wait five seconds, and try again — the BMS resets passively on this platform.
Charger won't recognise the pack after storage
Li-ion packs stored discharged can drop below the charger's acceptance voltage — typically around 2.5V per cell. When cell voltage falls that low, the Worx charger refuses to begin a charge cycle and either blinks an error or shows no response. To recover, apply a brief low-current trickle charge using a compatible lab charger set to 0.1C until the pack reaches 3.0V per cell. Once above that threshold, the standard Worx charger will recognise the pack and complete the charge normally.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: Worx
- Manufacturer: CS
- Series: Standard
- Color: Black
- Product Type: Li-ion
- Battery Type: Li-ion
- Warranty: 12 Months
- Bulk Orders: sales@batteryweb.com
Frequently Asked Questions
My WU137 drill cuts out the instant I pull the trigger on a tough screw — battery seems fine otherwise. What's happening?
That's a BMS overcurrent trip caused by motor-start inrush current. When the drill hits a high-resistance load, the current spike in the first milliseconds of trigger pull exceeds the pack's protection threshold and the circuit opens. Release the trigger, wait five seconds for the BMS to reset, then re-engage under lighter load. If it trips repeatedly on normal fasteners, check the bit contact and gearbox for drag — excess mechanical resistance amplifies the inrush spike.
The tool feels underpowered and bogs badly when I'm driving long screws or cutting thick material — battery charges fine and shows full. What causes this?
That's voltage sag — under sustained high-current draw, the battery's terminal voltage drops enough that the tool loses torque even though the pack shows a full charge at rest. The most common cause on 12V platforms is high contact resistance at the battery rail terminals, especially on older tool bodies with worn or corroded contacts. Clean the battery contacts on both the pack and the tool with a dry cloth or fine abrasive, then reseat the pack firmly. If sag persists, check whether the pack's resting voltage reads at or above 12.6V with a multimeter — a pack measuring below 12V at rest has cell-level capacity loss.
After leaving my WU161 in the van overnight in winter, the battery charges up but the tool has noticeably less power until it warms up. Is the battery damaged?
No damage — this is normal Li-ion behaviour below 5°C. Cold temperatures raise the internal resistance of lithium cells significantly, which limits how much current the pack can deliver on demand and reduces effective torque output. Once the pack warms to room temperature, performance returns to normal. To avoid this, store the battery indoors overnight rather than in the vehicle, and let the pack sit at room temperature for at least 20 minutes before use in cold conditions.
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