Optus E5377 Mobile Hotspot Replacement Battery 3.7V 1700mAh

Optus E5377 — 3.7V Li-ion Replacement Battery

This is a 3.7V 1700mAh lithium-ion battery for the Optus E5377 portable Wi-Fi hotspot. It restores power capacity when the original cell has degraded and the device no longer holds a usable charge. Dimensions are 65.10 × 45.70 × 5.30mm — confirm these match your existing battery before fitting.

• E5377 hotspot platform: The E5377 runs a combined cellular modem and multi-device Wi-Fi radio from a single cell. Both radios draw simultaneously, so the battery must handle sustained current draw rather than short bursts. This cell meets that voltage and footprint requirement.
• Bench tested on actual hardware: We ran this cell under simultaneous modem and Wi-Fi load. The BMS held voltage without dropping into protective cutoff, and charge acceptance on a standard USB source was clean with no thermal flags.
• Ventilation during long sessions: When connected devices are at range or signal is weak, the cellular radio runs at maximum output power. Place the hotspot on an open surface — not inside a bag or pocket — during extended sessions to stop heat building at the battery.

Why the E5377 drops connections mid-session under maximum device load

The E5377 manages two simultaneous RF loads — the cellular modem and the Wi-Fi access point. When five or more client devices are active, combined current draw spikes sharply. If the battery cell cannot sustain that draw, voltage sags briefly below the BMS threshold and the hotspot cuts power to the modem to protect the cell. The result is a sudden disconnect for all connected users, even though the device appears to still be on. A fresh cell with full capacity handles these draw spikes without the voltage sag that triggers the cutoff.

E5377 won't power on after sitting unused for several weeks

Li-ion cells self-discharge during storage. If the E5377 sat unused long enough, the battery may have dropped below the minimum boot voltage — typically around 3.0V — and the BMS will block startup to prevent cell damage. Plugging in a charger and leaving it for 20–30 minutes before attempting to power on gives the BMS enough charge to re-enable the output circuit. If the device powers on during charging but not on battery alone, the cell has degraded past recovery and needs replacement.