Siemens A31 Compatible Battery EBA-660 3.7V 600mAh Li-ion

Siemens A31 / C65 / CXT65 Series — 3.7V Li-ion Replacement Battery (EBA-660)

This is a 3.7V, 600mAh Li-ion replacement battery for Siemens mobile phones including the A31, C65, CF62T, and CXT65 series. It replaces OEM part numbers EBA-660, EBA-670, EBA-760, and related variants. Physical dimensions are 51.60 × 39.97 × 4.50mm — confirm these against your compartment before ordering.

• A31, C65, CXT65 platform fit: These models share the same battery bay dimensions, connector pinout, and 3.7V nominal voltage rail across the series. One cell covers the full range because Siemens standardised the power interface across this mid-2000s handset lineup.
• Bench tested on actual hardware: We cycled this cell on a C65 handset. The BMS accepted charge without flagging a fault, voltage held at 3.7V nominal through the full cycle, and the protection circuit triggered correctly at low-voltage cutoff.
• First-cycle fuel gauge reset on the A31 and C65: After fitting this cell, run one full discharge to auto-off followed by a complete uninterrupted charge before normal use. The phone's fuel gauge IC was calibrated to your old cell's discharge curve — one full cycle lets it re-map to the new cell and stop reporting inaccurate percentages.

Sudden shutdown at 20–30% on the C65 and CXT65 after a cell replacement

This happens when the fuel gauge IC still holds the discharge curve of the original degraded cell. The new cell has a steeper voltage cliff under load — the phone's baseband radio draws a short current spike during a call or network search, voltage drops below the BMS cutoff threshold, and the phone shuts off even though the displayed percentage looks safe. The fix is a full calibration cycle: discharge the phone to auto-shutdown, then charge uninterrupted to 100%. After one complete cycle the fuel gauge re-maps its coulomb counter to the new cell and the false cutoffs stop.

Phone warm near the battery compartment during first charge

A new Li-ion cell has slightly higher internal impedance than a broken-in cell, so the charge IC dissipates more energy as heat during the first one or two cycles. On the A31 and C65 this shows up as warmth at the back cover near the battery bay — not the charging port. It typically resolves by the second or third charge cycle as impedance settles. If the phone stays hot past 40°C or the warmth moves toward the screen, stop charging and check that the battery is seated flat with no edge pressure on the contacts.