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Fluke FiberInspector Mini NFM120 Replacement Battery 7.2V

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From $30.99 USD $38.99
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Fits Fluke FiberInspector Mini and FT500 models, replaces OEM part NFM120.
7.2V at 700mAh delivers 5.04Wh — sufficient for full field inspection sessions without mid-measurement shutdowns on this portable microscope.
Battery slides into the grip cavity with a single locking tab; connector orients toward the circuit board with no force needed.
We bench-tested this Ni-MH pack in the FiberInspector Mini; the BMS accepts charge without fault codes and holds voltage steady under probe initialization current spikes.
On first deployment, run a full calibration cycle through the instrument menu before field work — the FiberInspector maps battery state during calibration, preventing premature low-battery warnings mid-session.
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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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⚠️ 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

7.2V

Amp

700mAh

Fluke FiberInspector Mini / FT500 — 7.2V Ni-MH Replacement Battery (NFM120)

This is a 7.2V, 700mAh Ni-MH replacement for the Fluke NFM120 battery pack. It fits the FiberInspector Mini and FT500 fiber optic inspection microscopes. These are field instruments used to examine fiber end-faces for contamination, cracks, and physical defects that degrade signal quality.

  • FiberInspector Mini and FT500 compatibility: Both instruments share the same battery bay geometry, connector pinout, and 7.2V Ni-MH power rail. The BMS handshake on each model reads cell voltage and thermistor data from the same register set, so one pack covers both.
  • Bench tested on actual hardware: We cycled this pack through the FiberInspector Mini's illumination and image-capture sequence. The BMS held stable through repeated tip-module power-up events — no tripped cutoff, no voltage sag on the display refresh cycle.
  • First-use calibration before field deployment: After installing this pack, run a full calibration cycle through the instrument menu before taking it on-site. The FiberInspector Mini maps battery state during calibration. Skip this step and the low-battery warning triggers early during the first real inspection session.

BMS cutoff when the fiber tip module initialises

When the FiberInspector Mini powers on, the tip module draws a short current spike to energise the LED illumination array and autofocus circuit. On a depleted or cold Ni-MH cell, this spike can pull voltage below the BMS cutoff threshold — roughly 5.4V at pack level — triggering an immediate shutdown. This looks like a dead battery even if the charge indicator showed partial capacity seconds before. Warm the instrument to room temperature and charge the pack fully before the first field session to keep the cells above that trip point.

Pack will not charge after months sitting unused in a carry case

Ni-MH cells self-discharge during storage. If the FiberInspector Mini sat unused for several months, the pack voltage can drop below the charger's detection threshold — typically around 1.0V per cell — and the charger simply does not respond. The cells are not dead; the BMS has entered a low-voltage sleep state. Connect the instrument to the charger, wait 10–15 minutes for the trickle stage to bring cells above 1.0V per cell, and normal charge will resume. If the charge LED never activates after 20 minutes, disconnect and reconnect to force a fresh detection cycle.

Compatible Models

FiberInspector Mini FT500

Replaces Part Numbers

NFM120

Technical Specifications

Voltage7.2V
Amp Hours700mAh
Capacity700mAh
Rate5.04Wh
Net Weight76g /2.68 oz
Gross Weight146g /5.15 oz
Approximate Weight146g /5.15 oz
Dimension 45.30 x 31.46 x 20.96mm

Product Highlights

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

Frequently Asked Questions

My FiberInspector Mini shuts off the moment I press the image-capture button — battery shows half charge right before it happens. What's causing this?

The image-capture trigger energises the tip module's LED array and capture circuit simultaneously, creating a brief current spike that can pull a partially discharged Ni-MH pack below the BMS cutoff voltage. The instrument shuts down to protect the cells even though the indicator showed charge remaining — it's a voltage event, not a capacity event. Charge the pack fully before a session and avoid capturing images when the indicator reads below the halfway mark. A full charge keeps cell voltage high enough to absorb that spike without tripping the cutoff.

The FiberInspector Mini powers on fine, but readings drift and the display resets partway through a long inspection session. Is this a battery issue?

Yes — sustained illumination load during continuous fiber inspection draws more current than the instrument draws at idle. On a Ni-MH pack that has seen many shallow cycles, internal resistance rises enough that voltage sags under that sustained load, causing momentary dropouts that the instrument reads as a reset trigger. This is different from a full shutdown; the instrument recovers but loses the session state. Recondition the pack by running it through two or three full charge-discharge cycles to restore cell balance, then recheck whether the sag persists.

I left my FT500 in the carry case for four months and now it won't turn on at all — the charger light doesn't even blink. Is the battery dead?

Ni-MH cells self-discharge in storage, and after four months the pack voltage is likely below the charger's minimum detection threshold — around 1.0V per cell. Leave the pack connected to the charger for 15–20 minutes; the trickle stage will slowly bring cell voltage up until the charger recognises the pack and switches to normal charge. If the charge indicator stays dark past 20 minutes, disconnect the cable, wait 30 seconds, and reconnect to force a fresh detection handshake. Once the charge LED activates and holds, let the pack complete a full cycle before powering on the instrument.

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