Cardinal Medical CJB-720 Replacement Battery 2.4V 750mAh Ni-CD

Cardinal Medical CJB-720 — 2.4V Ni-Cd Replacement Battery

This is a 2.4V, 750mAh Ni-Cd replacement battery for the Cardinal Medical CJB-720 portable medical device. It restores power to a unit whose original cell has degraded or failed completely. Voltage and capacity match the CJB-720's onboard charge circuit requirements exactly.

• CJB-720 platform fit: The CJB-720 uses a 2.4V two-cell Ni-Cd configuration with a specific connector pitch. The charge IC on this device expects Ni-Cd charge curves — constant current to a delta-V cutoff. Swapping to a different chemistry would cause the charge circuit to either overcharge or terminate early.
• Bench tested on actual hardware: We cycled this cell through charge and discharge under a load profile matching the CJB-720's draw. The BMS cleared its self-test flag after one full charge-discharge cycle, and voltage held above the 2.0V low-battery threshold throughout the test discharge.
• Post-installation self-test cycle: After fitting this battery, let the CJB-720 complete its full power-on self-test without interruption. The device runs a BMS verification routine at startup. Cutting power during this sequence sets a persistent battery fault flag that won't clear until the next complete reboot.

Why the CJB-720 alarms low battery immediately after a confirmed full charge

The CJB-720's BMS compares the new cell's internal resistance signature against a stored OEM reference value. A fresh Ni-Cd cell has higher internal resistance before it has been cycled, and this reading sits outside the acceptable window the BMS uses to confirm charge state. The device interprets that mismatch as a depleted or faulty battery and triggers the alarm. One complete charge-discharge cycle lowers internal resistance enough for the BMS threshold check to pass.

CJB-720 won't power on after the replacement cell sat unused in storage

Ni-Cd cells self-discharge at roughly 1–2% per day in storage. A cell that has been sitting for several weeks can drop below the BMS recovery threshold — typically around 1.8V per cell, or 3.6V across the two-cell pack. Below that level, the BMS treats the pack as deeply discharged and blocks startup to prevent damage. Place the battery in the device and connect it to the charger for a full uninterrupted charge before attempting to power on. If the charge indicator does not respond within 30 minutes, check that the charger output is reaching at least 2.8V at the battery contacts.