About this replacement
Motorola DROID ULTRA / XT1080 — 3.8V Li-Polymer Replacement Battery (EU20 / SNN5924A)
This is a 3.8V, 2100mAh lithium-polymer replacement battery for the Motorola DROID ULTRA, XT1080, XT1080M, and DROID MAXX smartphones. It slots into the original battery bay using the same form factor as the OEM cell. Capacity is 2100mAh (7.98Wh) — identical to the factory specification.
- XT1080 and DROID MAXX platform fit: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The EU20 and SNN5924A part numbers cover the full XT1080 variant stack, including the XT1080M carrier build.
- Bench tested on actual hardware: We cycled this cell through a full discharge-charge sequence on an XT1080 unit. The BMS accepted the cell without a protection trip, and the charge IC negotiated correctly at the standard 3.8V nominal rail.
- Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.
Sudden shutdown at 20–30% on the DROID ULTRA after a cell swap
This happens when the fuel gauge IC is still calibrated to the old cell's discharge curve. The reported percentage does not match the new cell's actual voltage under load. When the modem fires a high-draw burst or the screen brightness peaks, the cell voltage drops below the BMS cutoff threshold even though the OS shows charge remaining. One full discharge-charge cycle forces the coulomb counter to reset against the new cell's actual capacity.
OS reporting wrong battery percentage after replacement
The XT1080 stores learned capacity data in the fuel gauge IC — that data references the old, degraded cell. After swapping in a fresh 2100mAh cell, the IC uses stale calibration, so the percentage readout drifts or jumps erratically. Drain the battery fully until the phone shuts off, then charge to 100% without interruption. After one complete cycle the coulomb counter recalibrates and the percentage stabilises.