Netgear AirCard 815S Replacement Battery W-9 3.8V 4300mAh

Netgear AirCard 815S / 791S Series — 3.8V Li-ion Replacement Battery (W-9)

This 3.8V 4300mAh Li-ion battery replaces the OEM W-9 cell in the Netgear AirCard 815S, AirCard 791S, AirCard 791L, and Explore 815S mobile hotspots. These are portable LTE hotspot devices — they create a Wi-Fi network for connected devices using a cellular data connection. Voltage and capacity match OEM spec exactly.

• AirCard 815S and 791S compatibility: Both the 815S and 791S share the same battery bay dimensions, 3.8V power rail, and W-9 part number. The BMS handshake protocol is identical across the series, so one cell works across all listed models without modification.
• Bench tested on actual hardware: We ran this cell under a combined cellular modem and Wi-Fi radio load — the closest simulation to real hotspot use. The BMS held steady through connection bursts and throttled correctly at low-voltage cutoff rather than hard-cutting the session.
• Ventilation during extended sessions: Keep the hotspot on a hard, flat surface rather than in a pocket or bag during long sessions. When connected devices are far from the hotspot, the cellular radio runs at maximum output power — that extra heat goes directly into the battery cell and accelerates wear.

Why the AirCard 815S drops all connected devices mid-session

When several devices are active simultaneously, the modem and Wi-Fi radio both draw peak current at the same time. This combined load can pull the cell voltage below the BMS protection threshold for a fraction of a second — enough to trigger a shutdown. A worn or degraded cell has higher internal resistance, making the voltage sag deeper and faster under the same load. A fresh cell at full capacity handles the current spike without hitting cutoff. If drop-outs persist on a new battery, reduce connected devices to isolate whether it is a load issue or a firmware issue.

Hotspot shows charging but will not boot after sitting in a drawer

After extended storage, a Li-ion cell can self-discharge below 3.0V — the minimum voltage the hotspot needs to initialise its boot sequence. The device may show a charging indicator because the USB circuit is active, but the CPU will not start until the cell climbs above the boot threshold. Leave it on charge for at least 30 minutes before pressing the power button. If it still does not boot, check that the charger is delivering the correct 5V output — an underpowered USB source will trickle-charge too slowly to recover a deeply discharged cell.