AT&T AirCard 779S W-8 Replacement Battery 3.7V 2000mAh

AT&T AirCard 779S — 3.7V Li-ion Replacement Battery (W-8)

This is a 3.7V, 2000mAh Li-ion battery for the AT&T AirCard 779S mobile hotspot. It fits the AirCard 779S, AirCard 779S 4G, and AC779S variants. Swap it in when the original battery no longer holds enough charge to keep the hotspot running through a full session.

• AirCard 779S family fit: The 779S, 779S 4G, and AC779S all share the same battery bay dimensions and connector pinout. Part numbers W-8, W-7b, and 308-10004-01 are cross-references for the same physical cell — one battery covers the whole group.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the 779S platform. The BMS communicated cleanly with the hotspot's fuel gauge, and the device reported battery percentage accurately from the first cycle.
• Ventilation during extended hotspot sessions: Keep the 779S on a hard, flat surface with airflow around it during long sessions. When connected devices are at the edge of signal range, the cellular radio runs at peak output — the battery absorbs that heat directly, which accelerates cell degradation over time.

Hotspot cutting connected devices mid-session on a new battery

When five or six devices are connected simultaneously, the 779S pulls from the cellular modem and the Wi-Fi radio at the same time. That combined draw can pull the battery voltage below the BMS protection threshold momentarily, triggering a brief shutdown even on a charged cell. The fix is to reduce the number of active connected devices, or move the hotspot closer to the cell tower to lower modem transmit power. At lower transmit demands, the voltage sag is shallow enough that the BMS stays open and the session holds.

AirCard 779S won't power on after sitting unused for several weeks

Li-ion cells self-discharge at roughly 2–3% per month under ideal conditions — faster if stored warm. After several weeks unused, the 779S battery can drop below the minimum boot voltage the device requires to start. Plug the hotspot into USB power and leave it connected for at least 20–30 minutes before pressing the power button. If the charge indicator does not respond within that window, the cell has likely dropped below 2.5V and needs a slow pre-charge cycle — leave it on charge for a full hour before attempting to boot.