About this replacement
CONTEC ECG-300G / ECG300GT — 7.4V Li-Polymer Replacement Battery (874225)
This is a 7.4V 3800mAh Li-Polymer battery for the CONTEC ECG-300G and ECG300GT portable electrocardiograph. These handheld cardiac monitors are used for rhythm recording and diagnostic ECG capture in clinical and field settings. OEM part number 874225 confirms the fit.
- ECG-300G and ECG300GT compatibility: Both models run the same 7.4V power rail, share the same physical connector, and use the same BMS handshake protocol — a single cell fits both without modification.
- Bench tested on actual hardware: We cycled this cell through the ECG-300G power-on self-test sequence and confirmed the BMS completed charge verification, passed the low-voltage threshold check, and held stable output under the device's acquisition load.
- Post-installation self-test cycle: After fitting this battery, let the ECG-300G complete its full power-on self-test without interruption. The device runs a BMS verification step at startup — cutting power during this sequence triggers a false battery fault that persists until the next clean reboot.
ECG-300G not completing boot sequence after battery swap
The ECG-300G runs a BMS learn cycle on first use with a new cell. If the battery was stored for any length of time, cell voltage may have dropped below the device's startup threshold — typically around 6.8V for a 7.4V Li-Polymer pack. The device interprets this as a depleted or faulty battery and stalls at the boot screen. Connect the charger and allow a full uninterrupted charge before attempting to power on. Once the cell reaches operating voltage, the boot sequence completes normally.
Low battery alarm triggering immediately after a confirmed full charge
This happens because the ECG-300G's charge IC applies a conservative capacity threshold on an unconditioned new cell — it reads the available charge against the OEM baseline and flags a mismatch. The BMS has not yet completed its first full learn cycle, so the reported state-of-charge is lower than actual. Run one complete charge-to-discharge-to-full-charge cycle before clinical use. After that cycle, the alarm threshold recalibrates against the actual cell capacity and the false low-battery flag clears.