OEM-127 Replacement Battery 3.7V 300mAh Li-Polymer

Custom Battery Pack OEM-127 — 3.7V Li-Polymer Replacement Battery

This is a 3.7V, 300mAh (1.11Wh) Li-Polymer replacement battery for devices designated OEM-127. The cell measures 35.90 × 23.90 × 4.30mm and is built for compact portable electronics where board space and weight are tightly constrained. If the original cell no longer holds adequate charge, this is the direct replacement.

• OEM-127 platform fit: The OEM-127 form factor uses a flat Li-Polymer cell at 3.7V nominal. Devices on this platform specify a specific footprint and connector orientation — the 35.90 × 23.90 × 4.30mm dimensions match that envelope without requiring case modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS protection circuit responded correctly to charge termination at 4.2V and activated low-voltage cutoff at the expected floor, with no anomalous heat during the conditioning cycle.
• First-cycle calibration on OEM-127: If the host device uses an integrated fuel gauge, it will read the new cell's state of charge against old calibration data. Run one complete charge-to-full, discharge-to-cutoff cycle immediately after installation so the gauge resets its capacity baseline to the new cell.

Pack running below 3.7V rated voltage on first use

Li-Polymer cells ship at storage voltage — typically 3.6V to 3.85V — not at full charge. That is not a fault. The cell needs one full charge cycle before it reaches and holds 4.2V at the top of range. Connecting to the host device before charging will show a lower voltage reading and may trigger a low-battery warning immediately. Charge fully via the OEM charger before first use to bring the cell to its rated operating window.

Device not reaching full charge on the first cycle

On the first charge cycle, the charge IC inside the host device or charger may apply a reduced current to condition new cells — this is standard CC/CV behaviour on Li-Polymer packs. The result is a longer charge time and sometimes an early termination that leaves the cell at 90–95% rather than 100%. This clears after one complete cycle as the charge IC updates its internal current and voltage targets. If the issue persists beyond cycle two, verify the charger output is within the cell's rated charge voltage of 4.2V.