Arlo Ultra Compatible Battery A-4a 3.85V 4800mAh

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

This is a 3.85V, 4800mAh Li-ion cell built to replace the original A-4a battery in the Arlo Ultra and Ultra 4K UHD wireless security cameras. It fits VMS5140 and VMA5400-10000S units along with four additional models in the same Ultra lineup. Voltage and capacity match OEM spec exactly — no adapter, no modification needed.

• Ultra series compatibility: Every model in this group runs the same 3.85V power rail, uses the same magnetic charge contacts, and communicates with the same BMS handshake sequence. Swapping the cell does not require re-pairing the camera hub — the hardware recognises the same voltage profile on contact.
• Bench tested on actual hardware: We cycled this cell through the Ultra's BMS under motion-triggered recording loads, including back-to-back IR LED activations. The protection circuit held within spec on both overcurrent and low-voltage cutoff thresholds throughout testing.
• First-install power cycle: After fitting the battery, trigger a full power cycle through the Arlo app — remove the camera from the base station view, reinsert it, and let firmware re-register the cell. Without this step, the motion recording scheduler can fail to log clips correctly to cloud storage.

Camera going offline in the app after a battery swap

The Arlo Ultra stores a session token tied to active power state. Pulling the battery clears that token, and the base station marks the camera as offline rather than waiting for re-authentication. This is a firmware behaviour, not a battery fault. Open the Arlo app, go to Device Settings, and use the Sync button to force a fresh handshake — the camera should come back online within 60 seconds at a clean 3.85V resting charge.

App showing 0% or wrong battery percentage after install

The Arlo Ultra uses a voltage-threshold indicator, not a fuel gauge IC. It maps percentage to discrete voltage steps, so a freshly installed cell at partial charge can read 0% or jump erratically until the firmware calibrates. Run one full charge cycle through the magnetic base — charge to 100%, let the camera operate through at least one full discharge — and the percentage readout will track the actual voltage curve correctly from that point forward.