AT&T IFWA-40 Compatible Battery 3.7V 3000mAh BAT-40

AT&T IFWA-40 — 3.7V Li-ion Replacement Battery (BAT-40)

This 3.7V 3000mAh Li-ion battery replaces the BAT-40 in the AT&T IFWA-40 Wireless Internet Wi-Fi Hotspot Router and Home Phone Base 4G LTE. It slots directly into the hotspot and restores standalone operation — no wall outlet needed. Capacity is 3000mAh (11.1Wh), matching the original specification.

• IFWA-40 platform fit: The IFWA-40 runs a combined 4G LTE modem and dual-radio Wi-Fi stack off a single 3.7V cell. The BAT-40 footprint, connector, and BMS handshake match exactly — the device firmware recognises the cell and reports charge level correctly without any workaround.
• Bench tested on actual hardware: We ran this cell under simultaneous modem and Wi-Fi load with multiple client devices connected. The BMS held the discharge curve steady and did not trigger a low-voltage cutoff during sustained throughput sessions.
• Cellular signal and battery load: In areas with weak 4G signal, the modem boosts transmit power automatically — this draws significantly more current than normal. Position the IFWA-40 near a window or elevated surface to reduce transmit power demand and reduce heat buildup on the cell.

Why the IFWA-40 drops connected devices mid-session on a new battery

The IFWA-40 runs its 4G modem and Wi-Fi radio simultaneously, and peak current draw spikes sharply when multiple clients are active at once. If the battery cell has high internal resistance — even when new — voltage can sag below the BMS cutoff threshold during those spikes, triggering a momentary shutdown. A genuine Li-ion cell with low internal resistance stays above the cutoff under combined load. Check that the battery contacts are clean and seated fully — a loose connection adds resistance and makes voltage sag worse.

IFWA-40 shows solid red light and won't power on after sitting unused

A solid red or no-boot condition after storage almost always means the cell dropped below the minimum boot voltage — typically under 3.0V for a 3.7V nominal Li-ion cell. Most Li-ion chargers will not begin a charge cycle on a cell this depleted and simply show no activity. Connect the hotspot to the OEM charger and leave it for 20–30 minutes without attempting to power it on — the charger needs time to trickle-charge the cell back above 3.0V before normal charging begins. If the device still shows no response after 45 minutes on charge, check the charger output voltage with a multimeter — it should read between 4.2V and 5.2V at the connector.