Siemens EBA-540 SX1 Replacement Battery 3.7V 1200mAh

Siemens SX1 / SX1 McLaren — 3.7V Li-ion Replacement Battery (EBA-540)

This is a 3.7V, 1200mAh Li-ion replacement battery for the Siemens SX1 and SX1 McLaren smartphones. It replaces OEM part numbers EBA-540, N6501-A100, and V30145-K1310-X260. When the original cell degrades and can no longer hold a stable charge, this unit restores power to both SX1 variants.

• SX1 and SX1 McLaren compatibility: Both handsets share the same physical bay, connector pinout, and 3.7V nominal voltage rail. The BMS communication protocol is identical across the two variants, so one cell covers both without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the SX1 platform and monitored the BMS handshake at each stage. The protection circuit triggered correctly at low-voltage cutoff, and charge acceptance was stable across multiple cycles.
• Fuel gauge recalibration on first use: On first use after installation, disable any fast-charge accessory and run one full discharge-to-charge cycle. This lets the SX1's fuel gauge IC map the new cell's discharge curve before reporting percentage — skipping this step often causes erratic readings on the status bar.

Sudden shutdown at 20–30% on the SX1 after a cell swap

The SX1's fuel gauge IC retains the discharge curve from the old, degraded cell. When a fresh cell is installed, the IC's stored curve no longer matches actual cell voltage under load. The modem and display draw combined pull voltage down faster than the IC predicts, triggering a hard shutdown before the displayed percentage reaches zero. One full discharge-charge cycle forces the coulomb counter to rebuild its reference against the new cell, and the shutdowns stop.

SX1 showing 100% immediately after install, then dropping fast

This is the fuel gauge IC reading from its last calibration point rather than the actual cell state. The IC was tuned to a worn cell with lower capacity, so it maps 1200mAh as "full" incorrectly and overshoots early. The fix is a single uninterrupted charge from under 5% to a full charge with the phone off or on standby — no calls or data sessions during that cycle. After one clean cycle, the displayed percentage should track actual capacity without sudden drops.