Siemens ST55 Compatible Battery EBA-595 3.7V 750mAh

Siemens ST55 / ST60 / ST50 — 3.7V Li-ion Replacement Battery (EBA-595)

This is a 3.7V, 750mAh Li-ion replacement battery for the Siemens ST55, ST60, and ST50 mobile phones. All three handsets share the same battery bay dimensions and connector, so one cell covers the range. OEM part numbers EBA-595, V30145-K1310-X268-1, L36880-N6851-A300, and N6851-A300 all cross-reference this cell.

• ST55, ST60, and ST50 compatibility: These three Siemens handsets use the same 64 × 46 × 8mm battery bay, identical connector pitch, and the same BMS handshake voltage threshold. Swapping between models is not an issue — the protection circuit board responds the same way across all three.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the ST55 platform. The BMS held charge termination at the correct 4.2V cutoff and triggered undervoltage lockout cleanly at 3.0V — no false trips under normal load.
• Fuel gauge recalibration on first use: After fitting this cell, run one full discharge to automatic shutdown, then charge uninterrupted to 100% before normal use. The ST55 fuel gauge IC was calibrated to your original cell's discharge curve — one complete cycle rewrites that baseline against the new cell and stops erratic percentage readings.

Sudden shutdown at 20–30% on the ST55 after a cell swap

The ST55's fuel gauge IC tracks capacity using a coulomb counter that was tuned to the internal resistance profile of the original cell. A new cell has a different impedance curve, so the counter reaches its low-voltage trip point earlier than the displayed percentage suggests. Under screen or radio load, the cell voltage sags briefly below the BMS cutoff threshold — the phone shuts off even though the gauge still shows charge remaining. One full discharge-charge cycle lets the coulomb counter relearn the new cell's curve. After that cycle, shutdowns at 20–30% should stop.

ST55 not powering on after the replacement battery sat in storage

Li-ion cells self-discharge during storage. If this battery shipped or sat unused long enough to drop below approximately 2.5V per cell, the BMS enters lockout mode and blocks current flow entirely — the phone shows nothing when you press the power button. Connect the phone to a charger and leave it for 15–20 minutes without attempting to power it on. Most charger ICs on these handsets apply a trickle pre-charge current that slowly walks the cell voltage back above the BMS re-enable threshold, typically around 2.9V. Once the screen shows a charging indicator, the BMS has released lockout and normal charging resumes.