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Testo 350 Flue Gas Analyzer Compatible Battery 8.4V 3500mAh

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From $57.99 USD $71.99
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Fits Testo 350, 350 Plus, 350-S, and 350-XL analyzers; replaces OEM part 0515 0098.
8.4V and 3500mAh capacity sustains field combustion analysis sessions without mid-measurement shutdown.
Ni-MH chemistry pack slots into standard battery compartment with positive terminal contact alignment.
We bench-tested this cell on a 350-S unit; BMS accepted full charge cycle with stable voltage delivery under sustained probe initialization load.
After installing, run a full calibration cycle through the instrument menu before field deployment — the analyzer maps battery state during calibration, and skipping this step causes premature low-battery warnings on the first measurement session.
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🔹 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.

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

Voltage

8.4V

Amp

3500mAh

Testo 350 Series — 8.4V Ni-MH Replacement Battery (0515 0098)

This 8.4V 3500mAh Ni-MH battery replaces the original pack in the Testo 350, 350 Plus, 350-S, and 350-XL flue gas analysers. It fits the standard battery bay without modification and connects via the same multi-pin interface as the OEM unit. The 29.4Wh capacity keeps the analyser powered through extended combustion measurement sessions in the field.

  • 350 series compatibility: The 350, 350 Plus, 350-S, and 350-XL share the same 8.4V battery rail, connector pinout, and BMS communication protocol. One pack covers the full platform.
  • Bench tested on actual hardware: We cycled this pack through the Testo 350 charge and discharge sequence and confirmed the BMS handshake cleared correctly. The pack accepted a full charge and held stable voltage under simulated probe module load without triggering a cutoff event.
  • Post-install calibration: After installing this pack, run a full calibration cycle through the instrument menu before taking it to site. The 350 maps battery state during calibration — skipping this step causes premature low-battery warnings on the first measurement session, even with a fully charged pack.

BMS lockout after the Testo 350 sat unused in a carry case for months

Ni-MH cells self-discharge slowly during storage. If the analyser sat unused long enough, the pack voltage can drop below the BMS recovery threshold — typically around 6V for an 8.4V Ni-MH pack. When that happens, the instrument may not power on at all, or it may appear to charge but show no progress. Connect the analyser to the charger and leave it for at least two hours before attempting to power on — the BMS needs time to trickle-charge the cells back above the recovery threshold before it will allow a normal charge cycle.

Testo 350 shutting down mid-measurement when the probe module initialises

When the 350's probe module powers up, it draws a brief current spike as sensors initialise. On a degraded or partially discharged pack, that spike can pull voltage low enough to trip the BMS undervoltage cutoff — shutting the instrument down before a single reading is logged. This is not a fault in the battery or the instrument; it is a protection response to a momentary voltage sag. Charge the pack to full before field deployment and confirm resting voltage is at or above 8.4V before connecting the probe module.

Compatible Models

350 350 Plus 350-S 350-XL Flue Gas Analyser 350 EPA 350-S Flue Gas Analyse 350-XL Flue Gas Analyse

Replaces Part Numbers

0515 0098 7HT-4/FAU 0515.0098

Technical Specifications

Voltage8.4V
Amp Hours3500mAh
Capacity3500mAh
Rate29.4Wh
Net Weight380g /13.40 oz
Gross Weight450g /15.87 oz
Approximate Weight450g /15.87 oz
Dimension 68.60 x 68.20 x 32.00 mm

Product Highlights

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

Frequently Asked Questions

The Testo 350 powers on fine but shuts off the moment it starts logging data from the probes — is this a battery fault?

This is a voltage-sag cutoff, not a dead battery. Under sustained sensor load during a logging session, a partially discharged or aged Ni-MH pack drops voltage faster than the BMS allows. The instrument shuts down to protect the measurement circuit. Charge the pack fully and confirm resting voltage reads at or above 8.4V on a multimeter before starting a logging session.

The new pack won't charge after the analyser sat in storage — the charger light comes on but nothing happens.

Ni-MH cells self-discharge during storage, and if voltage dropped below the BMS recovery threshold the pack enters a protection lockout. The charger sees the pack as unresponsive because the BMS is blocking the charge circuit. Leave the analyser connected to the charger for a minimum of two hours without interruption — the BMS trickle-charges the cells back above the threshold before allowing a normal charge cycle to begin.

After fitting the new battery, the Testo 350 shows a low-battery warning almost immediately even though the pack was charged before installation.

The 350 maps battery state during its calibration routine, and if that calibration was not run after fitting the new pack, the instrument is referencing voltage-threshold data from the old cells. Go into the instrument menu and run a full calibration cycle — this resets the battery state mapping to the new pack's voltage curve and clears the false low-battery indication.

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