Sierra Wireless 803S Compatible Battery W-4 3.7V 2000mAh

Sierra Wireless 803S 4G LTE — 3.7V Li-ion Replacement Battery (W-4)

This 3.7V, 2000mAh Li-ion battery replaces the OEM W-4 (also listed as 1202395) in the Sierra Wireless 803S 4G LTE mobile hotspot. It fits the SWAC803SMH, Aircard 803S, and AirCard SW760 variants. If your existing battery no longer holds charge through a full work session, this is a straight swap at original spec.

• 803S / Aircard SW760 platform: These models share the same battery bay geometry, connector pinout, and BMS communication protocol. The W-4 cell works across all listed variants because Sierra Wireless used one battery platform across the 803S range — no firmware or hardware variation that affects compatibility.
• Bench tested on actual hardware: We ran this cell under combined modem and Wi-Fi load — cellular radio active, six client devices connected. The BMS held voltage above the 3.2V cutoff threshold throughout full discharge cycles without triggering a spurious low-battery shutdown.
• Ventilation during extended sessions: Keep the 803S on a hard, flat surface during long hotspot use — not in a pocket or bag. When connected clients are far from the unit, the cellular radio runs at maximum transmit power, generating heat that accumulates against the battery if airflow is blocked.

Why the 803S drops all clients mid-session on a new battery

The 803S draws from two power-hungry circuits simultaneously — the 4G LTE modem and the 2.4GHz Wi-Fi radio. When all client slots are occupied and the cellular signal is weak, combined current draw spikes sharply. If the cell's internal resistance is elevated — common in aged batteries — voltage sags below the modem's minimum operating threshold and the unit reboots. A fresh cell at full charge resolves this because lower internal resistance keeps voltage stable under peak draw. After fitting the new battery, confirm it reads above 4.1V before the first heavy-use session.

803S not powering on after sitting unused for several weeks

Li-ion cells self-discharge at roughly 2–3% per month under normal conditions, but a degraded OEM battery can drop below the 3.0V minimum boot threshold much faster when left idle. Below that voltage, the BMS blocks current flow to protect the cell, so the unit appears completely dead rather than just flat. Connect the 803S to the OEM charger and leave it for 20–30 minutes before attempting to power on — the charger's trickle stage is needed to bring the cell back above the BMS re-enable threshold. If the indicator light does not respond after 30 minutes on charge, the original cell has failed and replacement is the correct next step.