BoostMobile AirCard 779S Compatible Battery 3.7V 2400mAh

BoostMobile AirCard 779S — 3.7V Li-ion Replacement Battery

This 3.7V, 2400mAh Li-ion battery fits the BoostMobile AirCard 779S mobile hotspot and its variants — the AirCard 779S 4G, AC779S, and NTGR779ABB. It slots into the same cavity as the original cell and connects to the same BMS interface. Capacity is rated at 8.88Wh.

• AirCard 779S variant compatibility: The 779S, 779S 4G, AC779S, and NTGR779ABB all share the same battery bay dimensions and 3.7V single-cell architecture. The BMS handshake is identical across these SKUs, so one cell works across the entire family without firmware mismatch.
• Bench tested on actual hardware: We ran this cell under combined cellular modem and Wi-Fi radio load at maximum connected devices. The BMS held voltage above the 3.2V cutoff threshold throughout the discharge cycle and showed no spurious low-battery shutdowns.
• Ventilation during extended sessions: Keep the 779S flat on a hard surface with its vents unobstructed during long hotspot sessions. When the cellular radio is pushing maximum output — common in weak signal areas — heat builds at the battery. A blocked vent accelerates cell aging faster than cycling does.

Why the AirCard 779S drops all connected devices mid-session

The 779S runs two power-hungry systems simultaneously — the 4G LTE modem and the Wi-Fi radio. At maximum client connections, combined draw can cause voltage to sag below the BMS protection floor, triggering an abrupt shutdown that looks like a Wi-Fi drop to connected devices. An aged original battery with elevated internal resistance hits this sag point much earlier in the discharge curve. A fresh cell with lower internal resistance sustains the voltage rail long enough for the BMS to stay clear of the cutoff threshold under that same combined load.

AirCard 779S won't boot after sitting unused for weeks

Li-ion cells self-discharge at roughly 2–3% per month at room temperature. If the 779S sat stored with a partially depleted battery, the cell can drop below the minimum boot voltage — typically around 3.0V — and the device will not respond to the power button. Plugging into the charger first is the correct step, but if the cell is too far discharged, the charger's pre-charge circuit must bring it back above 3.0V before the hotspot firmware will initialise. Leave it on charge for at least 20 minutes before attempting to power on.