FEIN ASCT 18 Replacement Battery 18V 4000mAh Li-ion B18A.165.01
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FEIN ASCT 18 Replacement Battery 18V 4000mAh Li-ion B18A.165.01 - 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.
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Disclaimer
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🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.
FEIN ASCT 18 Replacement Battery 18V 4000mAh Li-ion B18A.165.01 - is backordered and will ship as soon as it is back in stock.
Voltage
18V
Amp
4000mAh
FEIN ASCT 18 Series — 18V Li-ion 4000mAh Replacement Battery (B18A.165.01)
This 18V 4000mAh Li-ion battery replaces the FEIN B18A.165.01 and compatible OEM references including 92604175020 and 92604179020. It fits the ASCT 18, ASCT 18 M, ASCM 18, ASCM 18 QX, and more than ten additional FEIN 18V platform tools. Voltage is 18V nominal; capacity is 4000mAh (72Wh) as confirmed by product data.
- FEIN 18V platform fit: The ASCT 18 family and ASCM 18 series share the same 18V battery rail, connector pinout, and BMS handshake protocol. One battery pack spans cutting, sanding, and scraping tools across the range without adapter changes.
- Bench tested on actual hardware: We ran this pack through full charge and load cycles on FEIN 18V tooling. The BMS held overcurrent protection thresholds during motor-start inrush on the multi-tool oscillating head and did not false-trip under sustained cutting load.
- Break-in load cycling on the ASCT 18: On first use, run the multi-tool at half load — light sanding or shallow cuts — for two full discharge and recharge cycles before pushing maximum torque applications. This lets the BMS profile the motor's inrush current draw and calibrate overcurrent thresholds before heavy scraping or plunge cuts.
BMS overcurrent trip on trigger-pull inrush — why the ASCT 18 cuts out instantly
The ASCT 18 oscillating mechanism draws a brief high-current spike the moment the trigger fires. On a new or freshly charged pack, a BMS that has not yet profiled this inrush can interpret the spike as a fault and open the protection circuit immediately. The result is a dead pack that recovers within seconds but trips again on the next trigger pull. Running two half-load break-in cycles allows the BMS to set a wider overcurrent window that matches the motor's actual start signature.
Tool bogs and loses torque mid-cut — voltage sag under sustained load
Voltage sag happens when the cells cannot deliver current fast enough to maintain the rail voltage under sustained motor draw — common during long scraping runs or aggressive material removal. Corroded or loosely seated battery contacts increase internal resistance and worsen sag, making the problem appear earlier in the charge cycle than it should. Remove the pack, clean the gold-contact terminals on both the battery and tool body with isopropyl alcohol, and reseat firmly. If the tool still bogs, check rail voltage under load — a healthy pack should stay above 16.5V during continuous use.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: FEIN
- 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 FEIN ASCT 18 cuts out the instant I pull the trigger — why does a new battery do this?
This is a BMS overcurrent trip caused by the motor-start inrush spike on the oscillating head. A new pack's BMS has no current-draw profile for this motor yet, so it treats the spike as a fault and opens the protection circuit. Run the tool at light load — gentle sanding or shallow cuts — for two full charge and discharge cycles. After that, the BMS calibrates its threshold to the ASCT 18's actual inrush signature and the cut-outs stop.
The charger's LED is blinking red and won't accept this pack — what's happening?
After storage, cell voltage can drop below the charger's acceptance threshold, which is typically around 2.5V per cell. Most chargers refuse to begin a normal charge cycle on a pack that reads below this floor and signal it with a red blink. Leave the pack at room temperature for 30 minutes, then reconnect — some FEIN chargers include a recovery or "wake-up" mode that trickle-charges at low current until the pack reaches 3.0V per cell before switching to full charge. If the charger still rejects it after two attempts, measure pack voltage at the terminals — it should read at least 15V across the 18V pack to enter a normal charge cycle.
The ASCT 18 runs noticeably weaker in cold weather — is the battery faulty?
Not faulty — Li-ion internal resistance rises sharply below 5°C, which reduces how much current the cells can deliver and causes earlier voltage sag under load. The ASCT 18's motor draw is high enough that even a moderate resistance increase translates to a clear loss of torque and shorter working time. Store the battery at room temperature and only move it to the tool just before use — a warm pack in a cold environment performs far better than one that has been sitting in an unheated workshop overnight. If performance does not recover once the pack warms back above 10°C, check terminal contact resistance as a secondary cause.
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