About this replacement
Physiomed VocaSTIM / Vocastim Trainer — 8.4V Ni-MH Replacement Battery (HR-AAA4U-1000-F3+F4)
This 8.4V, 740mAh Ni-MH battery replaces the factory cell in the Physiomed VocaSTIM and Vocastim Trainer. Both devices are portable medical speech stimulation units used in clinical speech therapy and vocal rehabilitation. This cell matches the OEM voltage, connector, and BMS communication requirements for those platforms.
- VocaSTIM and Vocastim Trainer compatibility: Both models share the same battery bay geometry, 8.4V supply rail, and connector pinout. The BMS on both units reads cell chemistry via the same thermistor line, so a correctly spec'd Ni-MH replacement passes the handshake without triggering a battery fault.
- Bench tested on actual hardware: We ran this cell through charge-discharge cycles on a Ni-MH analyser and confirmed the BMS accepted the cell without false fault flags. Capacity delivery at the 740mAh rating was consistent from cycle three onward once the cell chemistry stabilised.
- Power-on self-test protocol: After installing this cell, let the VocaSTIM complete its full startup self-test without interruption. Medical device BMS firmware runs a battery verification routine at boot — cutting power mid-sequence causes a persistent false battery fault that will not clear until the next complete power cycle from a rested state.
VocaSTIM not completing boot sequence after battery swap
The VocaSTIM runs a BMS learn cycle during its first few boots on a new cell. If the device stalls or alarms during startup, the most likely cause is the BMS flagging the new cell as unverified — this is normal behaviour with a fresh Ni-MH replacement. The BMS on this unit is calibrated for OEM chemistry tolerances and applies a conservative threshold on first contact with a new cell. Complete one full charge from flat, then allow the device to boot without interruption. By the second or third cycle, the BMS accepts the cell and the startup sequence completes normally.
Low battery alarm triggering immediately after a confirmed full charge
A freshly charged replacement cell can still trigger the low battery alarm on the VocaSTIM if the BMS has not yet completed its learn cycle. Ni-MH cells have a slightly different internal resistance profile when new, and the BMS voltage threshold comparison can read this as an undercharged state. This is not a faulty battery — it resolves after one full charge-discharge cycle. Charge the cell completely, allow the device to discharge through normal use, then recharge to 100% before returning to clinical use.