About this replacement
Cefar Activ X 4 / Rehab X 4 — 4.8V Ni-MH Replacement Battery (REHABX4)
This is a 4.8V, 2000mAh Ni-MH replacement battery for the Cefar Activ X 4 and Rehab X 4 portable electrotherapy units. It uses OEM part number REHABX4 and fits directly into the device battery compartment. The Activ X 4 and Rehab X 4 share the same battery housing, connector, and voltage rail — one battery covers both models.
- Activ X 4 and Rehab X 4 compatibility: Both units run the same 4.8V Ni-MH cell pack with identical BMS handshake requirements and connector orientation. The shared platform means one part number covers both device variants without modification.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the Cefar platform. The BMS accepted the cell without fault codes, completed its verification routine, and held stable voltage across the therapeutic output channels.
- Post-swap self-test care: After fitting this battery, allow the Activ X 4 to complete its full power-on self-test without interruption. Cutting power during that startup sequence triggers a battery fault flag that persists until the device is fully rebooted and the self-test runs again from the beginning.
Low battery alarm during active therapy on a freshly charged cell
The Cefar Activ X 4 monitors cell voltage in real time during stimulation output. On a new Ni-MH cell, internal resistance is slightly higher in the first few cycles, which causes a brief voltage sag under load. The device BMS reads this sag as a low-battery condition and triggers the alarm even when the cell is fully charged. Run one complete charge-discharge cycle before clinical use — this lowers internal resistance and brings the resting voltage into the range the BMS expects.
Device will not power on after the battery sat unused in storage
Ni-MH cells self-discharge at roughly 1–3% per day. A cell stored for several months can drop below the BMS recovery threshold — typically around 4.0V for a 4.8V pack — at which point the device will not boot at all. Place the battery on charge for a full cycle before attempting to power on the device. If the charger does not recognise the cell initially, leave it connected for 15–20 minutes to allow the charge IC to detect sufficient voltage and begin the recovery charge.