About this replacement
Fluke Raytek Raynger 3i Plus — 3.7V Li-ion Replacement Battery (4422324)
This 3.7V Li-ion cell replaces OEM part 4422324 in the Fluke Raytek Raynger 3i Plus infrared thermometer. At 2600mAh (9.62Wh), it fits the handheld non-contact temperature measurement unit used across HVAC, electrical, and industrial maintenance workflows. The cell slots into the battery compartment and connects to the instrument's onboard BMS via the standard pack contacts.
- Raynger 3i Plus platform fit: The 3i Plus uses a single-cell Li-ion pack at 3.7V nominal. The instrument's BMS reads pack voltage and thermistor data through the contact array. This replacement carries the same pin-out and thermistor circuit, so the instrument completes handshake without throwing a battery error on boot.
- Bench tested on actual hardware: We ran this cell through the Raynger 3i Plus charge cycle and triggered the optical sensor module repeatedly to load the output rail. The BMS held regulation through sustained spot-check sequences and cut off cleanly at low-voltage threshold without dropping the display mid-read.
- Post-install calibration on the Raynger 3i Plus: After fitting this cell, run a full calibration cycle through the instrument menu before field deployment. The Raynger 3i Plus maps battery state during that calibration pass. Skipping it causes premature low-battery warnings on the first measurement session even when the cell is fully charged.
Raynger 3i Plus shutting down mid-measurement with a charged cell
The optical sensor module in the Raynger 3i Plus draws a brief current spike each time it initialises — higher than the steady-state display load. If the cell voltage is sitting at the lower end of the nominal range, this spike can push the BMS into a momentary undervoltage cutoff. The instrument interprets that as a dead battery and shuts down, even if the state-of-charge indicator showed adequate charge. A freshly charged cell starts above 4.1V, which gives enough headroom to absorb the probe initialisation draw without tripping the threshold.
Pack will not charge after the instrument sat unused in a carry case for months
Li-ion cells in low-use instruments self-discharge slowly over storage. If the Raynger 3i Plus sat unused for several months, the cell may have dropped below the BMS recovery threshold — typically around 2.5V — and the protection circuit locks out charging entirely. Plugging in the charger shows no charge activity and the instrument does not power on. Place the instrument on the charger and leave it connected for at least 30 minutes without interruption; most BMS circuits include a recovery trickle mode that brings the cell back above the lockout threshold before switching to normal CC/CV charging. If voltage recovers to 3.0V or above, the full charge cycle will complete normally.