About this replacement
H-Wave H4 / OTC — 7.2V Ni-MH Replacement Battery (OSA476)
This is a 7.2V, 2000mAh Ni-MH replacement battery for the H-Wave H4 and OTC portable electrotherapy units. It replaces OEM part OSA476 and restores full power delivery to the device's electrical nerve stimulation circuits. Capacity matches the original specification — 14.4Wh total energy.
- H4 and OTC platform fit: Both units share the same battery bay geometry, connector pinout, and BMS handshake protocol. The OSA476 cell format is identical across both models, so one part number covers either device without modification.
- Bench tested on actual hardware: We cycled this cell through the H4's full charge-discharge sequence and confirmed the BMS accepted state-of-charge readings correctly from cycle one. Charge termination triggered cleanly at full capacity with no false cutoff events.
- Power-on self-test handling: After installing the battery, let the H4 complete its startup self-test cycle without interruption. The device runs a BMS verification pass at boot — cutting power mid-sequence causes the unit to log a battery fault that persists until the next clean reboot.
Why the H4 trips a low-battery alarm on a freshly charged OSA476
The H4's BMS uses a voltage threshold calibrated to an aged OEM cell's charge curve. A new Ni-MH cell delivers a slightly different voltage profile during the first few cycles, which can sit outside the BMS's expected window. The device reads this as a low-charge condition even when the battery is fully charged. Running one complete charge-discharge cycle lets the BMS learn the new cell's actual resting voltage and clears the alarm permanently.
H4 won't power on after battery sat unused in storage
Ni-MH cells self-discharge during storage — if the OSA476 sat for several months before installation, its resting voltage may have dropped below the H4's BMS recovery threshold. At that point the device won't boot because the BMS treats the voltage as an unsafe deep-discharge state. Place the battery in the H4 and connect the charger for a full charge cycle before attempting to power on. If the charger accepts the cell and completes normally, resting voltage will return to the 7.2V operating range and the unit will boot.