About this replacement
JVC GZ-HD620 Series — 3.7V Li-ion Replacement Battery (BN-VG138)
This 3.7V, 4450mAh Li-ion battery replaces the OEM BN-VG138 cell in JVC HD camcorders. It fits the GZ-HD620, GZ-HD620BAH, GZ-HM330, GZ-MS210, and over 170 additional GZ-series models. Same voltage rail, same connector, same BMS communication protocol as the original.
- GZ-series platform fit: JVC's GZ-series camcorders share a common battery bay, connector pinout, and BMS handshake across the HD and MS sub-lines. That shared architecture means one cell covers a wide model range without any hardware modification.
- Bench tested on actual hardware: We ran this cell in a GZ-HD620 body through charge, discharge, and BMS communication cycles. The protection circuit responded correctly to charge termination and over-discharge cutoff without triggering false low-battery warnings mid-recording.
- First-use charge cycle on GZ-series bodies: Run the first full charge inside the GZ-series camera body or JVC OEM charger — not a third-party charger. The body's BMS maps voltage thresholds to the battery-remaining display during that initial cycle. Skipping it causes the indicator to read inaccurately for the life of the cell.
Why the GZ-HD620 shows a dead battery icon on a freshly charged replacement cell
The GZ-HD620 uses a voltage-curve mapping system to estimate remaining charge. A new third-party cell has a slightly different discharge curve than the original JVC cell the firmware was calibrated against. On first install, the camera reads an unfamiliar voltage profile and defaults to a low or empty indicator as a safety fallback. One full charge cycle completed inside the camera body resets that mapping. After that cycle, the indicator tracks accurately.
Battery percentage jumping erratically during GZ-series recording
Erratic percentage jumps during active recording come from the BMS recalibrating against a discharge curve it hasn't fully learned yet. Video recording, continuous autofocus, and image stabilisation create variable current draw — the BMS samples voltage under load and compares it to its stored curve. Until the curve is calibrated, those load spikes cause sudden percentage drops and recoveries. Run two full discharge-to-recharge cycles in the camera body to stabilise the readings; the display should settle at or above 3.5V per cell before the camera cuts out.