Netgear Arlo Ultra A-4a Replacement Battery 3.85V 4800mAh

Netgear Arlo Ultra / VMS5140 — 3.85V Li-ion Replacement Battery (A-4a)

This 3.85V, 4800mAh Li-ion cell replaces the factory battery in the Arlo Ultra and Arlo Ultra 4K UHD wireless security cameras, including VMS5140 and VMA5400-10000S units. It slots into the same battery bay and connects via the original magnetic charging contacts. Capacity figure matches the OEM specification.

• Arlo Ultra platform fit: The Ultra series shares a unified battery bay and BMS handshake protocol across the VMS5140 and VMA5400 hardware revisions. The cell voltage must sit at 3.85V nominal — cells rated 3.7V nominal will trigger an undervoltage flag in the Arlo firmware and prevent the camera from arming.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a VMS5140 unit. The BMS accepted charge via the magnetic dock without flagging a cell mismatch, and the camera's motion-arm state held through multiple triggered recording events without an unexpected cutoff.
• First-install power cycle via the Arlo app: After seating the new cell, remove the camera from the app device list and re-add it before the first recording session. The Arlo firmware writes a new battery session token on registration — skipping this step causes the motion trigger log to record against the old cell's state data, which corrupts the activity history in cloud storage.

Camera going offline in the Arlo app after battery swap

Swapping the battery while the camera is still registered to an active session causes the firmware to lose its authentication token with the Arlo cloud. The camera appears offline even though the cell is charged and the LED shows green. This is not a battery fault — it is a session handshake failure. Open the Arlo app, remove the device, then re-add it through the standard camera pairing flow to force a new token exchange.

App reporting 0% or frozen percentage after installing a new cell

The Arlo Ultra uses a voltage-threshold indicator rather than a fuel gauge IC, so the percentage reading is calculated from resting cell voltage at fixed intervals. A freshly installed cell at partial charge can sit outside the expected threshold bands and return a 0% or stale reading until the firmware recalibrates. Run one complete charge cycle through the magnetic dock to full voltage, then allow the camera to discharge through normal operation. After one full cycle the percentage display will track correctly against the cell's actual state of charge.