Siemens S25 Replacement Battery 3.7V 750mAh Li-ion

Siemens S25 / S2588 — 3.7V Li-ion Replacement Battery (V30145-K1310-X111-1)

This is a 3.7V 750mAh Li-ion battery for the Siemens S25 and S2588 mobile phones. It replaces part number V30145-K1310-X111-1 and fits directly into the original battery bay. Use this when the existing cell no longer holds charge or fails to power the phone.

• S25 and S2588 fitment: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. One cell fits both. No adapter or modification needed.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the S25 platform. The BMS accepted the cell without fault flags, and the protection circuit tripped correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first cycle: After fitting this battery, disable fast charging for the first full discharge-to-charge cycle. The fuel gauge IC on the S25 is calibrated against the old cell's discharge curve. Running one uninterrupted cycle at standard current lets it map the new cell before fast charge introduces higher current into an uncalibrated state.

Sudden shutdown at 20–30% on the Siemens S25 after a cell swap

This happens because the phone's fuel gauge IC is still using the discharge curve from the old, degraded cell. The new cell has a steeper voltage drop near the bottom of its charge window. When the modem transmits or the backlight peaks, current draw pulls the cell voltage below the shutdown threshold before the percentage reading catches up. The fix is one full uninterrupted discharge-to-charge cycle with no fast charge. After that cycle, the fuel gauge recalibrates and the percentage readings align with actual cell voltage.

Phone warm near the battery slot during the first charge after installation

A fresh cell starts with higher internal impedance than a broken-in one. During early charge cycles, the charge IC works harder to push current through that impedance, and the heat is a byproduct of that resistance. This is normal for the first two to three cycles and reduces as the cell breaks in. If the phone stays warm past three full cycles, check that the charge IC is not stuck in a high-current mode — on the S25, pulling the battery for ten seconds and reseating it resets the charge controller to its default current profile.