About this replacement
Lenovo 300w Gen 3 / 500w Gen 3 — 11.52V Li-Polymer Replacement Battery (L20C3PG0)
This is an 11.52V, 3900mAh (44.93Wh) Li-Polymer battery for the Lenovo 300w Gen 3 and 500w Gen 3 (Intel) series laptops. It replaces OEM part numbers L20C3PG0, L20D3PG0, L20L3PG0, L20M3PG0, and several 5B11B and SB11B variants. If your original cell no longer holds a charge or the laptop only runs on AC power, this battery matches the original voltage rail and connector..
- 300w and 500w Gen 3 compatibility: These models share the same three-cell Li-Polymer pack, 11.52V nominal rail, and BMS handshake protocol. The connector and physical footprint are identical across the 82J1 and 82J3 chassis variants covered under this listing.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a 300w Gen 3 unit. The BMS accepted the cell without fault codes, the charge controller stepped through CC/CV correctly, and the pack reached full capacity without throttling.
- Post-install discharge cycle: After fitting this battery, run one full discharge to hibernate-cutoff, then charge uninterrupted to 100%. This resets the BIOS battery learn cycle and clears the inaccurate health warning that appears on screen after a cell swap.
Why the 300w Gen 3 shuts down at 20–30% after a battery swap
The BIOS fuel gauge IC builds a capacity model against the old cell over many cycles. When a new cell goes in, that model is stale — it expects the voltage-to-capacity curve of the degraded original. The new cell's voltage at 25% state-of-charge looks like 5–10% to the old model, so the BIOS triggers an emergency shutdown even though real capacity remains. Two to three full discharge-recharge cycles let the fuel gauge IC re-learn the new cell's curve and correct the cutoff point.
BIOS showing wrong Wh rating or "unknown battery" after fitting a new cell
The Wh figure the BIOS displays is read from EEPROM data embedded in the battery pack, not calculated live from voltage and current. If the value shown differs from the rated 44.93Wh, the EEPROM on the new cell is reporting its design-rated value under a slightly different chemistry spec than the original. This is a display discrepancy only — it does not affect charge behaviour or actual capacity. To confirm the cell is functioning correctly, check that charge current is flowing and that the pack voltage reads between 11.1V and 12.6V under the BIOS hardware monitor.