Sierra Wireless 803S 4G LTE Replacement Battery 3.7V 3600mAh

Sierra Wireless 803S 4G LTE / AirCard SW760 — 3.7V Li-ion Replacement Battery (W-4,1202395)

This 3.7V, 3600mAh Li-ion battery replaces the original cell in the Sierra Wireless 803S 4G LTE mobile hotspot and AirCard SW760. It fits SWAC803SMH and AirCard 803S units as well. The battery slots into the same compartment and connects through the existing BMS contacts — no modification needed.

• 803S / AirCard SW760 platform fit: These models share the same 3.7V single-cell architecture, battery footprint, and BMS handshake protocol. One replacement cell covers the full range listed above.
• Bench tested on actual hardware: We ran this battery on the 803S with eight simultaneous connected clients and a weak LTE signal to force maximum modem output. The BMS held the discharge floor without tripping into protective cutoff, and the unit maintained stable 3.7V nominal through the draw cycle.
• Ventilation during extended sessions: Keep the hotspot in an open, ventilated spot when running multiple connected devices for long periods. The cellular radio ramps to full output power when signal is poor or clients are distant — that heat load concentrates directly on the battery cell and shortens its cycle life faster than any other single factor on this device.

Why the 803S drops connected clients mid-session at maximum load

The 803S modem and Wi-Fi radio draw simultaneously when the device is serving multiple clients. At peak load — eight clients plus a weak LTE signal — instantaneous current demand spikes hard. If the battery cell has degraded internal resistance, voltage sags below the BMS protection threshold and the unit cuts power briefly, dropping all connected devices. A fresh cell with lower internal resistance handles the combined draw without tripping the cutoff. If dropouts persist after installing this battery, check whether the device is sitting on a surface that blocks the rear vents — thermal throttling can produce identical symptoms.

803S not powering on after sitting unused for several weeks

Li-ion cells self-discharge at roughly 1–3% per month under normal storage, but the 803S draws a small standby current even when switched off — this accelerates depletion. If the cell drops below approximately 2.5V, the BMS locks the battery into deep-discharge protection mode and the unit will not boot. Plug the hotspot into the OEM charger and leave it connected for at least 90 minutes before attempting to power on — most BMS circuits require a slow trickle phase to exit protection mode before delivering full charge current. If the LED shows no charging activity after 15 minutes on charge, reseat the battery to re-establish contact with the BMS pins.