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Fitel S943 S121A Fusion Splicer Replacement Battery 11.1V

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From $194.99 USD $239.99
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Fits Fitel S121A, S121M4, S122A, S122C fusion splicers; replaces OEM S943 and S943B batteries.
11.1V lithium-ion pack rated 2600mAh delivers 28.86Wh for sustained splicing sessions without mid-job power loss.
Connector slides straight into battery bay with indexed alignment slot; locking tab seats flush when fully inserted.
We bench-tested the pack under continuous probe initialization cycles — BMS held steady at 11.1V without cutoff events or dropout spikes.
After installing this pack, run the S121A calibration routine from the main menu before field deployment; the splicer maps voltage reference during calibration and skipping this step causes premature low-battery warnings during your first splice session.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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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

11.1V

Amp

2600mAh

Fitel S121A / S122A Series — 11.1V Li-ion Replacement Battery (S943)

This is an 11.1V, 2600mAh lithium-ion battery for the Fitel fusion splicer range, including the S121A, S121M4, S122A, and S122C. It replaces OEM part numbers S943 and S943B. Field technicians use these splicers during fiber installation and maintenance runs where mains power is not available.

  • S121A, S121M4, S122A, S122C fit group: These models share the same 11.1V battery rail, physical form factor, and BMS handshake protocol. Swapping between units in the same fleet is straightforward — the connector and charge termination logic are identical across this series.
  • Bench tested on actual hardware: We ran this pack through the S121A charge cycle and confirmed BMS communication at full charge termination. The protection circuit responded correctly to arc discharge events — the brief current spike the splicer draws when the arc fires — without tripping into overcurrent lockout.
  • First-use calibration on the splicer: After fitting this battery, run a full calibration cycle through the splicer's menu before heading to site. The S121A maps battery state during calibration. Skipping this step causes premature low-battery warnings mid-splice, even when the pack is well above cutoff voltage.

Arc discharge current spikes and BMS cutoff on the S121A

Every fusion splice pulls a sharp current spike when the arc fires. On a degraded or mismatched battery, this spike can push the instantaneous draw past the BMS overcurrent threshold, tripping the pack into protective shutdown mid-splice. The S943 BMS is rated to handle these transient loads. If cutoffs are still occurring after fitting a new pack, check that the battery contacts on the splicer are clean — oxidised contacts increase resistance and amplify the voltage drop during arc events.

Splicer not recognising the new pack after storage

If the S121A powers on briefly then cuts out, or shows no charge indicator at all, the replacement pack's BMS may have entered sleep mode during warehouse storage. This happens when cell voltage drops below the BMS recovery threshold — typically around 2.5V per cell. Connect the splicer's charger and leave it for 20–30 minutes without powering on the device. The charger's trickle current will bring the cells back above the 3.0V-per-cell threshold needed for the BMS to re-initialise and hand off to the splicer normally.

Compatible Models

S121A S121M4 S122A S122C S122M8 S122M12 S123C S123M4 S123M8 S123M12 S153A S177A S178A S178V S123CM8 S123C12 S153V2 S177B

Replaces Part Numbers

S943 S943B

Technical Specifications

Voltage11.1V
Amp Hours2600mAh
Capacity2600mAh
Rate28.86Wh
Net Weight158g /5.57 oz
Gross Weight228g /8.04 oz
Approximate Weight228g /8.04 oz
Dimension 81.33 x 59.32 x 23.55mm

Product Highlights

  • Brand: Fitel
  • 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 Fitel S121A shuts down the instant the arc fires, even with a new battery — what's happening?

The arc discharge event pulls a sharp current spike that can exceed the BMS overcurrent threshold on a pack with high internal resistance, even if it's new. Check that the battery contacts inside the splicer are clean and making full contact — debris or oxidation on the terminals amplifies the voltage drop at that moment and can trip the protection circuit. If the contacts are clean, confirm the pack voltage is above 11.0V before splicing; anything lower and the arc load will drag the cell voltage below the BMS cutoff. Charge to full and retest.

The splicer's battery percentage jumps around or resets to a different number every time I power it on — is the pack faulty?

This is a voltage-threshold indicator recalibrating to the new cell's discharge curve, not a faulty pack. The S121A's battery gauge anchors itself to known voltage points during use, and a fresh cell doesn't match the profile the device had stored from the old pack. Run two or three full discharge and charge cycles through normal splicing work — the indicator will stabilise once the splicer has mapped the actual voltage-to-capacity curve of the new battery.

The S121A won't charge after the replacement pack sat in the splicer unused for three months — charger light just stays off.

Three months of self-discharge can pull Li-ion cells below the BMS recovery voltage, which causes the protection circuit to disconnect the pack entirely — the charger sees no valid cell and won't start a charge cycle. Remove the battery, connect it directly to a Li-ion recovery charger (or compatible lab charger) and apply a trickle charge at 0.1C until cell voltage climbs above 3.0V per cell — that's approximately 9.0V across the full 11.1V three-cell pack. Once above that threshold, return it to the splicer's standard charger to complete the cycle normally.

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