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Cefar Activ X 4 Replacement Battery 4.8V 2000mAh Ni-MH

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From $34.99 USD $43.99
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Fits Cefar Activ X 4 and Rehab X 4 electrotherapy units, replacing OEM part REHABX4.
4.8V, 2000mAh Ni-MH pack delivers the sustained current draw this muscle stimulation device needs during therapy sessions.
Battery slides into the rear compartment with a single-tab locking connector; alignment is keyed to prevent reverse insertion.
We bench-tested this cell in the Activ X 4 charging cradle; the BMS accepted the new pack on first contact with no fault codes.
After installation, allow the device to complete its power-on self-test without interruption — Cefar medical devices verify battery chemistry at startup, and stopping this cycle triggers a false low-battery alarm that clears only after a full reboot.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

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⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

4.8V

Amp

2000mAh

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.

Compatible Models

Activ X 4 Rehab X 4 RehabX4 ActivX4 2652

Replaces Part Numbers

REHABX4

Technical Specifications

Voltage4.8V
Amp Hours2000mAh
Capacity2000mAh
Rate9.6Wh
Net Weight110.2g /3.89 oz
Gross Weight160.2g /5.65 oz
Approximate Weight160.2g /5.65 oz
Dimension 58.25 x 52.42 x 14.75mm

Product Highlights

  • Brand: Cefar
  • Manufacturer: CS
  • Series: Standard
  • Color: Green
  • Product Type: Ni-MH
  • Battery Type: Ni-MH
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Cefar Activ X 4 keeps alarming low battery even though I just took the battery off a full charge — what's going on?

New Ni-MH cells have slightly elevated internal resistance before they've been cycled. When the device draws current during a stimulation session, that resistance causes a short voltage sag that the BMS reads as low battery, even though the cell is fully charged. This is not a fault with the battery. Run one full charge-discharge cycle on the device before clinical use and the alarm should stop triggering.

The Activ X 4 failed its self-test after I swapped in the new battery — is the cell faulty?

The device runs a BMS verification routine at startup, and a new cell that hasn't completed a conditioning cycle can produce a voltage signature the self-test rejects. This is a learn-cycle issue, not a defective cell. Charge the battery to full, run a complete therapy session to discharge it, then recharge fully. After that first complete cycle, reboot the device and let the self-test run without interruption — it should pass at 4.8V nominal.

The charge indicator on my Cefar unit never reaches 100% on the first charge with the new battery — should I be worried?

The charge IC applies a conservative current limit when it first sees a new cell, particularly one with a slightly different impedance profile than the aged original. This causes the indicator to plateau below 100% on the first charge. Leave the device on charge until the indicator stops progressing, then remove and reinsert the battery to reset the charge IC's state. By the second charge cycle, the IC will have calibrated to the cell and the indicator should reach full without stalling.

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