HB4H1 Replacement Battery Virgin Mobile VM820 3.7V 1000mAh

Virgin Mobile VM820 — 3.7V Li-ion Replacement Battery (HB4H1)

This is a 3.7V, 1000mAh Li-ion replacement battery for the Virgin Mobile VM820. It carries OEM part number HB4H1 and slots directly into the VM820's battery bay. Voltage and cell dimensions match the original spec: 59.67 × 39.66 × 4.26mm.

• VM820 fit: The VM820 uses a low-voltage 3.7V single-cell Li-ion pack with a compact footprint. This cell matches that voltage rail and physical profile, so the battery contacts seat correctly and the BMS handshake with the phone's charge IC completes without errors.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a VM820-class platform. The BMS held the charge termination cutoff at the correct upper voltage and the protection circuit tripped as expected at the low-voltage threshold — no overrun in either direction.
• Fuel gauge recalibration on first use: After installing a new cell, run one full discharge to near-empty then charge uninterrupted to 100% before using the phone normally. The VM820's fuel gauge IC needs a complete reference cycle to map its percentage readout against the new cell's actual discharge curve — skipping this causes erratic percentage jumps.

Why the VM820 reports wrong battery percentage after a cell swap

The VM820 tracks battery state through a fuel gauge IC that builds its percentage model from discharge data on the old cell. When a new cell goes in, that calibration data no longer matches the new cell's discharge curve. The phone reads voltage and maps it to a percentage based on stale reference points, so it can show 40% and shut down moments later. One full uninterrupted discharge-to-charge cycle resets the IC's reference and aligns percentage readouts to the actual cell capacity.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff failure, not a capacity problem. Under load — especially when the modem is active during a call or data transfer — the cell voltage drops sharply below the threshold the phone's protection circuit accepts, triggering an immediate shutdown even though the displayed percentage appears safe. Older fuel gauge calibration data makes the phone blind to how quickly this new cell's voltage sags under load. Force a full calibration cycle first; if shutdowns continue, check that cell voltage at rest reads at least 3.6V after a full charge.