About this replacement
Pulsar Axion XM / XQ Series — 3.7V Li-ion Replacement Battery (APS 3 / PL79161)
This 3.7V, 3400mAh Li-ion battery fits the Pulsar Axion XM, Axion XQ, Axion XQ LRF, and Digex thermal imaging monoculars. It slots into the battery compartment and powers both the thermal sensor core and the OLED display. Capacity is sourced from Pulsar's own OEM specification for the APS 3 cell.
- Axion XM, XQ, XQ LRF and Digex compatibility: These models share the same APS 3 form factor, 3.7V nominal rail, and battery contact layout. The onboard BMS in each device uses the same charge handshake, so one cell fits all listed variants without modification.
- Bench tested on actual hardware: We ran this cell through full charge cycles on the Axion XQ platform. The BMS accepted the cell immediately, charged to 4.2V at cutoff, and the thermal sensor initialised without fault flags on power-up.
- Field swap procedure for thermal monoculars: The Axion series stores last-used calibration offsets in non-volatile memory, so those persist across battery swaps. However, if the device shows a black screen after inserting this cell, press and hold the power button for three seconds — the display controller requires a full cold boot cycle on first use with a new battery.
Why the Axion XQ display shuts off mid-observation without warning
The Axion XQ's thermal sensor draws a spike of current whenever it runs a flat-field correction (FFC) cycle — this happens automatically every few minutes to recalibrate the microbolometer. An aged or partially discharged cell can dip below the BMS cutoff threshold during this spike, causing an immediate shutdown that looks like a random power loss. The fix is not a device fault — it is a cell that can no longer sustain the FFC current draw. A fresh cell at full charge clears this entirely.
Cell not recognised after insertion — charging LED does not activate
If the Pulsar charger or the device itself shows no charging activity after inserting this battery, the BMS protection circuit may have tripped during shipping or storage. Remove the cell, leave it out for 60 seconds, then reinsert — this resets the protection FET. If the charger still shows no activity, connect the cell to the Pulsar charger rather than charging via the device's USB port, as the USB path requires the device to be powered on first. The charger should read between 3.0V and 4.2V and begin the charge cycle within 30 seconds of insertion.