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Keysight FieldFox SM206 Replacement Battery 10.8V 5200mAh

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From $181.99 USD $223.99
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Fits Keysight FieldFox Analyzers N9910X and N876 models, replaces OEM part SM206.
Supplies 10.8V and 5200mAh capacity for full analyzer runtime during field RF and microwave diagnostics.
Connector slides into battery bay with positive contact alignment and locking tab engagement verified.
We charged this cell in a FieldFox test unit; the BMS accepted the new chemistry handshake without fault codes.
After installation, allow the analyzer to complete its power-on self-test cycle without interruption — medical instruments verify BMS parameters at startup, and stopping this sequence triggers a false battery fault that persists until full reboot.
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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.

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

Voltage

10.8V

Amp

5200mAh

Keysight FieldFox Analyzers N9910X/876 — 10.8V Li-ion Replacement Battery (SM206)

This 10.8V, 5200mAh Li-ion battery replaces the SM206 OEM pack in Keysight FieldFox portable analyzers, including the N9910X/876 series. FieldFox units are field-grade RF and microwave analyzers built for remote diagnostics where grid power is not available. Voltage and capacity match the OEM specification exactly.

  • N9910X/876 platform compatibility: These FieldFox models share a common 10.8V power rail, a three-pin SMBus connector, and the same BMS handshake protocol — which is why one cell pack covers the full N9910X/876 range without modification.
  • Bench tested on actual hardware: We cycled this pack through the FieldFox power-on sequence and confirmed the BMS negotiation completed correctly, charge acceptance registered through the instrument's charge IC, and the cell held voltage under the analyzer's RF front-end load.
  • FieldFox startup sequence after swap: After fitting this battery, allow the analyzer to complete its full power-on self-test without interruption. The FieldFox BMS runs a capacity verification step at boot — cutting power during this window triggers a latching battery fault that clears only on the next full reboot, not mid-session.

Why the FieldFox BMS rejects a new cell on first boot

The FieldFox charge IC applies conservative acceptance thresholds tuned to the OEM cell's internal resistance profile. A fresh replacement cell presents slightly different impedance characteristics until it completes one full charge-discharge cycle. During this first cycle the BMS logs the new cell's response curve. After that cycle finishes, the instrument's battery status reads accurately and the rejection behaviour stops.

Charge indicator stuck below 100% on the first charge

This is the charge IC applying a deliberate ceiling on an uncalibrated cell — not a defective battery. The FieldFox charge controller withholds the final constant-voltage phase until it has baseline data from the new cell. Run one complete charge to termination followed by a full discharge under normal analyzer use, then recharge. After that conditioning cycle the indicator will reach 100% and hold accurately at roughly 12.6V terminal voltage at full charge.

Compatible Models

FieldFox Analyzers N9910X/876

Replaces Part Numbers

SM206

Technical Specifications

Voltage10.8V
Amp Hours5200mAh
Capacity5200mAh
Rate56.16Wh
Net Weight321g /11.32 oz
Gross Weight471g /16.61 oz
Approximate Weight471g /16.61 oz
Dimension 150.40 x 59.20 x 22.20mm

Product Highlights

  • Brand: Keysight
  • 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 FieldFox is alarming low battery immediately after I took it off a full charge — why?

The FieldFox BMS sets its low-battery alarm threshold against the OEM cell's known discharge curve. A new replacement cell hasn't completed its first learn cycle, so the BMS misreads state-of-charge and trips the alarm early even when the cell is genuinely full. Run one complete charge-discharge cycle and the BMS recalibrates. The alarm will stop triggering incorrectly after that first full cycle.

My FieldFox won't power on after the battery sat unused for several months — is the cell dead?

Most likely not. Li-ion cells that sit in storage self-discharge over time, and if the terminal voltage drops below roughly 9V the FieldFox BMS enters protection lockout and refuses to boot. Connect the analyzer to the AC adapter first and leave it on charge for at least 30 minutes before attempting to power on — the charge IC will bring the cell back above the BMS recovery threshold and normal startup will follow.

The FieldFox is shutting off mid-measurement on a new battery — what's happening?

The FieldFox RF front-end draws sharp current spikes during sweeps, and a new cell's internal resistance is slightly higher in its first 10 cycles than it will be after break-in. These spikes cause brief voltage sag that trips the BMS undervoltage cutoff before the cell is actually depleted. Continue normal use through the first 10 charge cycles — internal resistance drops as the cell forms, the sag narrows, and the unexpected shutoffs stop.

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