CareFusion Med Systems III 3V Replacement Battery 2200mAh

CareFusion Med Systems III, 2860, 2863, 2865 — 3V Li-SOCl2 Replacement Battery

This is a 3V lithium-thionyl chloride cell rated at 2200mAh (6.6Wh), replacing the internal battery in the CareFusion Med Systems III infusion pump and the 2860, 2863, and 2865 series units. The battery powers the pump's control board, display, and alarm circuitry. Install only when the unit is powered down and service protocols allow field battery replacement.

• Med Systems III and 2860-series compatibility: These models share the same 3V control bus and physical cell format. The BMS in each unit reads the same voltage curve from a Li-SOCl2 cell, so one cell specification covers the full range without firmware or connector differences.
• Bench tested on actual hardware: We ran this cell against the Med Systems III load profile — control board active, display cycling, alarm circuit live. The BMS accepted the cell without fault codes, and the self-test sequence completed cleanly on the first boot after installation.
• Post-installation self-test protocol: After fitting this cell, allow the pump to complete its full power-on self-test without cycling power or interrupting the sequence. The BMS runs a voltage verification pass at startup — cutting power mid-sequence locks in a false battery fault that persists until the next clean reboot.

Why the Med Systems III BMS rejects a new Li-SOCl2 cell on first boot

Li-SOCl2 cells have a passivation layer that forms on the lithium anode during storage. On first load, this layer causes a brief internal resistance spike that the pump's BMS can read as a low-capacity or degraded cell. The pump may show a battery warning even though the cell is fully charged. One complete load cycle — powering the unit through a full operating session — burns off the passivation layer and brings the cell's voltage response back within the BMS acceptance window.

Low battery alarm triggers immediately after confirmed cell replacement

If the pump alarms low battery within seconds of a fresh cell install, the most likely cause is passivation-induced voltage sag — not a faulty cell. The BMS threshold on Med Systems III units is calibrated to OEM cell discharge curves, and a passivated cell's initial voltage drop can breach that threshold before the layer clears. Power the unit off, wait 30 seconds, then restart and allow the self-test to finish without interruption. If the alarm does not clear after one full operating cycle, verify the cell is seated fully and contact voltage reads at or above 3.0V at the terminals.