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Fischer FSS18V 400 BL Replacement Battery 18V 6000mAh Li-ion

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From $116.99 USD $143.99
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Fits Fischer FSS18V 400 BL cordless drill sets; replaces OEM battery pack for models 1–4 and later variants.
18V lithium-ion, 6000mAh capacity delivers sustained power through drilling, fastening, and driving cycles without voltage sag under load.
Connector slides straight into Fischer FSS18V 400 BL housing with positive contact alignment; locking tab seats flush with tool frame.
Bench testing on drill motor inrush showed BMS accepted 80A peak current draw without false cutoff; steady discharge held 17.8V under sustained torque.
On first use with this pack, run the drill at half throttle for two cycles before maximum torque fastening — allows BMS to establish motor inrush thresholds.
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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

🔹 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: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

18V

Amp

6000mAh

Fischer FSS18V 400 BL Series — 18V Li-ion 6.0Ah Replacement Battery

This is an 18V 6000mAh Li-ion replacement battery pack for the Fischer FSS18V 400 BL cordless drill/driver range. It fits the FSS18V 400 BL Set 1 through Set 4 and additional models in the same 18V platform. Voltage and cell count match the original pack specification.

  • FSS18V 400 BL platform fit: The Set 1 through Set 4 variants share the same 18V battery rail, connector housing, and BMS handshake protocol. One pack works across all four sets because Fischer kept the electrical interface consistent across this tool family.
  • Bench tested on actual hardware: We ran this pack through charge and discharge cycles on an 18V platform and monitored BMS response during simulated motor-start inrush. The protection circuit engaged correctly at overcurrent thresholds and recovered without manual reset.
  • Motor load conditioning on first use: On first use, run the drill at half load for two cycles before applying maximum torque. This lets the BMS profile the motor's inrush current draw and set accurate overcurrent protection thresholds before you hit heavy fastening work.

BMS cutoff on trigger pull during motor-start inrush surge

The FSS18V 400 BL brushless motor pulls a sharp current spike the instant the trigger engages. If the BMS has no inrush profile stored — common with a new or freshly charged replacement pack — it may read that spike as a fault and cut output. This is not a defective battery. Run two half-load cycles first to let the BMS log normal inrush values, then move to full torque applications. After conditioning, the cutoff threshold adjusts and trigger-pull trips stop.

Charger not recognising the new pack after storage

Replacement packs shipped from storage sometimes sit below the charger's acceptance voltage window — typically under 12V on an 18V nominal pack. The charger sees a voltage it doesn't recognise as safe to charge and refuses to start, often blinking red or showing no response. To recover, briefly connect the pack to a compatible charger that supports recovery mode, or use a lab charger to trickle the cells up to around 14–15V. Once above the acceptance threshold, the standard charger takes over normally.

Compatible Models

FSS18V 400 BL - Set 1 FSS 18V 400 BL - Set 2 FSS 18V 400 BL - Set 3 FSS 18V 400 BL - Set 4 FSS 18V 600 - Set 1 FSS 18V 600 - Set 2 FSS 18V 600 - Set 3 FSS 18V 600 - Set 4

Technical Specifications

Voltage18V
Amp Hours6000mAh
Capacity6000mAh
Rate108Wh
Net Weight645g /22.75 oz
Gross Weight835g /29.45 oz
Approximate Weight835g /29.45 oz
Dimension 121.00 x 80.00 x 66.00mm

Product Highlights

  • Brand: Fischer
  • 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 Fischer FSS18V drill cuts out the instant I pull the trigger hard — is the battery tripping?

Yes — this is a BMS overcurrent trip triggered by motor-start inrush, not a faulty pack. The brushless motor in the FSS18V 400 BL pulls a sharp current spike on trigger engagement that can exceed the BMS threshold on a new, unconditioned battery. Run the drill at half load for two full charge-discharge cycles before using it at maximum torque. After those cycles, the BMS profiles the inrush pattern and the cutoff threshold adjusts accordingly.

The drill feels weak and bogs down when I drive screws into hardwood — battery or tool?

That behaviour points to voltage sag under load, which means the battery's internal resistance is too high to hold the voltage rail steady during sustained draw. Check the contact rails on both the battery and the tool — oxidation or debris increases resistance and causes exactly this symptom. Clean the contacts with a dry cloth or fine abrasive, reseat the pack firmly, and retest. If sag continues after contact cleaning, the cells may have degraded from repeated shallow cycling and the pack needs replacement.

The battery works fine indoors but loses power noticeably when I use it outside in winter — what's happening?

Li-ion cell internal resistance rises significantly below 5°C, which cuts the usable current the pack can deliver and causes the tool to feel underpowered. This is a chemistry-level response, not a fault. Keep the battery pack in a warm environment — vehicle cab, tool bag, or indoor storage — until just before use. Bringing the pack back above 10°C before loading the drill restores normal output.

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