Siemens S45 Replacement Battery 3.7V 730mAh Li-ion

Siemens S45 / ME45 Series — 3.7V Li-ion Replacement Battery (V30148-K1310-X185-1)

This 3.7V Li-ion cell at 730mAh (2.7Wh) is a direct cell replacement for the Siemens S45, S45i, ME45, and 6618. It fits the original battery bay and connects via the standard Siemens three-contact terminal used across this GSM candybar range. Use the OEM part numbers V30148-K1310-X185-1, L36880-N4501-A100, V30148-K1310-X183, or V30145-K1310-X185 to cross-check fit before installing.

• S45 / ME45 platform compatibility: The S45, S45i, ME45, and 6618 share the same physical battery bay dimensions (55 × 36 × 8 mm), the same three-contact connector layout, and the same 3.7V charge profile. That shared hardware means one cell works across all four models without modification.
• Bench tested on actual hardware: We cycled this cell through the S45 charge circuit and confirmed the BMS accepted the full charge sequence without triggering an early cutoff. Charge current tapered correctly at top-of-charge, and the protection circuit tripped at the expected low-voltage threshold during discharge.
• Fuel gauge recalibration on first cycle: After fitting this cell, run one complete discharge down to automatic shutoff, then charge uninterrupted to 100% before normal use. The S45's fuel gauge IC was calibrated to the original cell's discharge curve — skipping this step causes the percentage counter to read inaccurately for several weeks.

Sudden shutdown at 20–30% on the S45 after a cell swap

The S45's baseband draws a hard spike of current each time the GSM radio transmits. A new cell with a slightly higher internal impedance than the aged original will sag in voltage under that load spike. If the voltage dips below the BMS cutoff threshold — even briefly — the phone shuts down despite the fuel gauge showing charge remaining. This is not a faulty cell; it is the fuel gauge IC reading a curve it has not yet learned. One full discharge-charge cycle lets the IC recalibrate, and the shutdowns stop. If they continue past three cycles, measure resting voltage — it should sit at or above 3.7V after a full charge.

Phone warm near the battery slot during the first charge

A new Li-ion cell typically has higher impedance than a broken-in cell, so the charge IC dissipates more heat during the constant-current phase of the first charge. On the S45, the charge IC sits directly adjacent to the battery bay, so warmth in that area during an initial charge is expected. It should be warm to the touch, not hot. If the phone becomes too hot to hold comfortably, remove it from charge and check that the contact pins are clean and seating flush — a poor contact forces the IC to compensate with higher voltage, generating excess heat.