Archos 55 Helium Ultra Replacement Battery 3.7V 2500mAh

Archos 55 Helium Ultra / A55 Helium — 3.7V Li-Polymer Replacement Battery (AC55HE)

This 3.7V, 2500mAh Li-Polymer cell replaces the original AC55HE battery in the Archos 55 Helium Ultra and A55 Helium smartphones. It targets devices that shut down unexpectedly, refuse to hold charge, or no longer power on after prolonged storage. Dimensions are 88.26 × 63.78 × 3.40mm — verify clearance before fitting.

• 55 Helium and A55 Helium compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol, making a single cell suitable for either variant. Voltage rail and thermistor line are identical across the two.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the Archos 55 Helium platform. The BMS accepted the cell without rejection flags, thermistor reporting stayed within spec, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Archos 55 Helium after a cell swap

This happens when the fuel gauge IC is still running the discharge curve from the old, degraded cell. The new cell has a steeper voltage cliff under modem and screen load than the old curve predicts. When the phone draws current for LTE or display wake, the cell voltage drops below the shutdown threshold before the gauge reads zero. One complete discharge cycle — draining to automatic shutdown, then charging uninterrupted to 100% — lets the coulomb counter reset against the real cell chemistry.

Phone reports erratic or jumping battery percentage after replacement

The fuel gauge IC on the Archos 55 Helium uses a learned model of the original cell's internal resistance and capacity. A new cell with different impedance throws that model off, causing percentage to jump — sometimes by 10–15 points — between readings. This is not a fault with the replacement cell. Force the IC to relearn by discharging the phone fully until it powers off automatically, then charging straight to 100% without interruption. After one complete cycle, percentage reporting stabilises.