Invivo Research 3155 Monitor Replacement Battery 12V 2300mAh

Invivo Research 3155 Monitor / Millennium 3500 Series — 12V Sealed Lead Acid Replacement Battery

This 12V, 2300mAh sealed lead-acid battery replaces the internal backup cell in Invivo Research portable patient monitors. It fits the 3155 Monitor, 3155A, Millennium 3500, and 3500U. These monitors run on external AC power in normal use — this battery kicks in during transport or power interruption to keep vital signs tracking uninterrupted.

• 3155 and Millennium 3500 platform compatibility: Both series share the same 12V sealed lead-acid internal backup architecture, connector pinout, and physical form factor. The charge management circuit in each unit expects SLA chemistry specifically — gel or AGM cells in this voltage class are not interchangeable here.
• Bench tested on actual hardware: We ran charge-discharge cycles on this cell and confirmed the BMS handshake completed without fault flags. The charge IC accepted the cell on first connection, and the monitor cleared its internal battery status register after one full cycle.
• Post-installation self-test cycle on Invivo monitors: After fitting this cell, let the device complete its power-on self-test without cutting power mid-sequence. These monitors run a BMS verification pass at startup. Interrupting it logs a false battery fault that will persist across reboots until a clean full-power cycle clears it.

Why the 3155 Monitor flags a battery fault after a confirmed full charge

Invivo monitors set their low-battery alarm threshold against a calibrated internal model tuned to an aged OEM cell. A new cell with slightly different internal resistance reads differently to the BMS during the self-test discharge pulse. This causes the monitor to log a fault even when state of charge is full. Running one complete charge-discharge cycle lets the BMS update its baseline. After that cycle, the alarm clears and does not return under normal load.

Monitor will not power on after the replacement cell sat in storage

Sealed lead-acid cells self-discharge at roughly 3–5% per month. A cell stored for several months before installation can drop below the BMS recovery threshold — typically around 10.5V for a 12V SLA cell — and the monitor will not boot. Connect the device to AC mains and leave it on charge for a full 16–24 hours before attempting to power on from battery alone. If the cell recovers above 11V on the charger, the BMS will accept it and the monitor will boot normally.