About this replacement
Compex Micro / Micro+ Series — 7.2V Ni-MH Replacement Battery (032002690)
This 7.2V 1800mAh Ni-MH battery replaces the original power cell in the Compex Micro, Micro+, Theta Stim, mi-Theta Pro, and 19 additional Compex electrostimulation devices. It matches the OEM voltage rail and connector footprint required by Compex's BMS. Capacity is 1800mAh (12.96Wh) — drawn directly from the product specification, not estimated.
- Micro and Theta Stim platform compatibility: These models share a common 7.2V Ni-MH architecture with a matched connector and BMS handshake protocol. Voltage tolerance on this platform is tight — cells outside the OEM voltage band trigger a hard fault on boot, so chemistry and nominal voltage must match exactly.
- Bench tested on actual hardware: We cycled this cell through the Compex boot sequence and BMS verification routine. The BMS accepted the cell without fault flags on the first full charge-discharge cycle, and charge current tapered correctly at the top-of-charge threshold.
- Startup self-test protocol: After installing this battery, allow the Compex device to complete its full power-on self-test without interruption. Compex units run a BMS verification check at startup — cutting power during this sequence causes a false battery fault that persists until the next clean reboot.
Why the Compex Micro triggers a low-battery alarm on the first charge cycle
Compex devices use a charge-acceptance threshold calibrated to the OEM cell's internal resistance profile. A new replacement cell has slightly higher internal resistance before the first full cycle, which the BMS reads as a low-state-of-charge flag. This is not a fault — it clears after one complete charge-discharge cycle. Run the device through a full cycle before drawing any clinical conclusions about battery health. After that cycle, the BMS learns the new cell and the alarm stops triggering.
Device will not power on after the battery sat unused in storage
Ni-MH cells self-discharge at roughly 1–2% per day. A cell stored for several months can drop below the BMS minimum recovery threshold — typically around 6.0V for a 7.2V Ni-MH pack — at which point the device will not respond to the power button at all. Place the battery on a compatible Compex charger and leave it connected for a minimum of 30 minutes before attempting to power on. If the charge indicator does not respond within 30 minutes, the cell voltage is likely below the charger's own detection floor and the cell requires a trickle pre-charge step before normal charging resumes.