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Anritsu MT9081 S331B Replacement Battery 10.8V 2100mAh

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From $118.99 USD $146.99
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Fits Anritsu S331B, S331C, S331D Site Master analyzers; replaces MT9081 Ni-MH battery pack.
10.8V 2100mAh Ni-MH chemistry delivers sustained power for extended field measurement sessions without voltage sag.
Connector slides into battery door slot with locking tab engaged; no tools required for installation.
We bench tested this pack on the S331B calibration cycle; BMS accepted load current without dropout or thermal throttle.
After installation, run a full calibration cycle through the instrument menu before field deployment — the S331B maps battery state during calibration, and skipping this step triggers premature low-battery warnings on the first measurement session.
Delivery time

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

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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

2100mAh

Anritsu S331B / S331C / S331D / S332B Series — 10.8V Ni-MH Replacement Battery (MT9081)

This is a 10.8V, 2100mAh Ni-MH replacement battery for the Anritsu Site Master cable and antenna analyzer series. It fits the S331B, S331C, S331D, S332B, and over 20 additional S-series handheld RF test instruments. The MT9081 part number is the standard OEM reference across this analyzer family.

  • S331 and S332 series compatibility: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One pack covers the full sweep of field-deployed Site Master units without modification.
  • Bench tested on actual hardware: We cycled this pack through the S331B charge circuit and confirmed the BMS handshake completes correctly. The cell temperature monitoring and cutoff thresholds responded within spec at both charge termination and low-voltage cutoff.
  • Pre-deployment calibration cycle: After fitting this pack, run a full calibration sequence through the Site Master's system menu before going to site. The instrument maps battery state during calibration — skipping this step causes the low-battery warning to fire early during the first measurement session, even with a fully charged pack.

BMS lockout after the S331B sat unused in a carry case for months

Ni-MH cells self-discharge steadily in storage. After several months in a case, cell voltage can drop below the BMS recovery threshold — at that point the pack refuses to accept a charge and the instrument shows no power response. The fix is to apply a low-current trickle charge directly to the pack terminals for 15–20 minutes using a compatible Ni-MH charger before inserting it into the analyzer. Once cell voltage climbs above approximately 9.0V, the BMS exits lockout and normal charging resumes through the instrument.

S331B shuts off mid-sweep during transmission line measurements

This is a voltage sag issue, not a dead pack. The Site Master's RF signal source draws a sharp current spike at sweep initiation — particularly at higher output power settings. If cells have aged or are partially discharged, that spike pulls the terminal voltage below the BMS cutoff threshold and the instrument drops out. Check resting voltage before a session: a healthy pack at full charge reads between 12.5V and 13.2V. If resting voltage is below 11.5V before powering on, recharge before attempting a measurement sweep.

Compatible Models

S331B S331C S331D S332B S332D S332A S113B S113C S114B S114C S251B S251C S325D S412D S810C S810D S820B S820C MT8212B MT9081 9081D MT9081D MT9082 MS2711B

Replaces Part Numbers

MT9081

Technical Specifications

Voltage10.8V
Amp Hours2100mAh
Capacity2100mAh
Rate22.68Wh
Net Weight315g /11.11 oz
Gross Weight465g /16.40 oz
Approximate Weight465g /16.40 oz
Dimension 144.85 x 51.37 x 19.73mm

Product Highlights

  • Brand: Anritsu
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

The S331B won't turn on after sitting in the truck for three months — is the battery dead or just locked out?

Almost always a BMS lockout from deep self-discharge, not a dead pack. Ni-MH cells lose charge in storage, and once voltage drops below the BMS recovery floor the instrument gets nothing and shows no response. Apply a low-current trickle charge directly to the battery pack — outside the instrument — for 15–20 minutes until terminal voltage climbs above 9.0V. Once the BMS exits sleep mode, reinsert the pack and charge normally through the Site Master.

Readings reset or freeze mid-logging session even though the battery indicator looks fine — what's happening?

This is a voltage dropout under sustained RF sweep load, not a display glitch. The Site Master's continuous sweep mode draws more current than the battery indicator tracks in real time — cell voltage sags under load, momentarily dropping below the processor's supply threshold, which resets the logging session. We saw this on the bench when cells were below 50% charge. Recharge the pack fully before long logging sessions and verify resting terminal voltage reads above 12.0V before starting.

The battery percentage on the S331B display jumps around after fitting a new pack — is something wrong?

Nothing is wrong with the pack. The Site Master's voltage-threshold fuel gauge is still calibrated to the old cell's discharge curve. A new Ni-MH pack has a flatter discharge profile than a worn cell, so the indicator reads erratically until the instrument recalibrates. Run two full charge-discharge cycles through the instrument and follow each with the calibration sequence in the system menu — after that the percentage display tracks accurately against the new pack's actual state of charge.

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