Sprint W-4 Replacement Battery 3.7V 3600mAh Li-ion 803S

Sprint 803S 4G LTE / Aircard 803S — 3.7V Li-ion Replacement Battery (W-4)

This is a 3.7V, 3600mAh Li-ion battery for the Sprint 803S 4G LTE mobile hotspot (also sold as the SWAC803SMH and Aircard 803S). It replaces OEM part numbers W-4 and 1202395. If your hotspot shuts down early, stops holding a charge, or won't power on after storage, this is the cell that needs swapping.

• 803S / SWAC803SMH / Aircard 803S fit: All three model names refer to the same hardware platform. They share the same battery bay dimensions, 3.7V rail, and BMS handshake protocol — this replacement drops straight in without firmware or connector issues.
• Bench tested on actual hardware: We cycled this cell under simultaneous modem and Wi-Fi load at maximum connected-device count. The BMS held voltage within spec across the full discharge curve and tripped the expected low-voltage cutoff without hard shutdowns or thermal events.
• Session heat management: Keep the 803S on a hard, flat surface during extended sessions — not in a pocket or case. When the cellular radio is operating at maximum output power chasing a weak signal, heat builds inside the enclosure and accelerates cell degradation over time.

Why the 803S drops connected devices mid-session under full load

The 803S runs two power-hungry subsystems simultaneously — the 4G LTE modem and the Wi-Fi radio. At maximum connected-device count, the combined current draw can cause voltage sag on a degraded or under-spec cell. When voltage dips below the BMS protection threshold, the device resets or disconnects all clients without warning. A fresh cell rated at the correct 3.7V, 3600mAh spec restores the headroom the BMS needs to stay above that cutoff under peak load.

803S won't power on after sitting unused for several weeks

Li-ion cells self-discharge at roughly 2–3% per month. If the 803S was stored with a low or partially depleted battery, the cell may have dropped below the minimum boot voltage — typically around 3.0V — triggering a deep-discharge lockout in the BMS. Placing a locked-out battery on charge sometimes recovers it if the BMS accepts a trickle-charge initiation, but cells that have sat below 2.5V for extended periods rarely recover to usable capacity. If the hotspot won't respond after 30 minutes on the charger, replace the battery and confirm the new cell reads at least 3.6V before attempting boot.