Alcatel OT-C825 Replacement Battery 3.7V 550mAh Li-ion

Alcatel OT-C825 / Elle No3 — 3.7V Li-ion Replacement Battery (T5000554AAAA)

This is a 3.7V, 550mAh Li-ion cell that replaces the original battery in the Alcatel OT-C825, OT-C835, Elle No3, and One Touch C825. It matches OEM part numbers T5000554AAAA, 3DSO9909AAAM, and B-K7. Capacity and voltage are identical to the factory cell these phones shipped with.

• OT-C825 / OT-C835 / Elle No3 platform fit: These models share the same battery bay dimensions (44.20 × 38.00 × 5.00mm), voltage rail, and connector pinout. One cell covers all of them without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on OT-C825 hardware. The BMS accepted the charge handshake on the first cycle, and the protection circuit tripped correctly at the low-voltage cutoff threshold during deep discharge simulation.
• First-cycle fuel gauge reset: After fitting this cell, run one complete discharge to near-shutdown, then charge uninterrupted to 100% before resuming normal use. The OT-C825 fuel gauge IC was calibrated to the old cell's discharge curve. Without one full cycle, the percentage readout can drift by 15–20 points.

Sudden shutdown at 20–30% on the OT-C825 after a cell swap

The OT-C825 uses a coulomb counter that tracks charge state relative to the old cell's internal resistance curve. A new cell has lower impedance, so the counter underestimates remaining charge — until the voltage drops sharply under modem or backlight load, triggering an immediate shutdown. This is not a fault in the replacement cell. Run two full discharge-charge cycles and the fuel gauge IC will converge on the correct discharge curve, eliminating the early cutoff.

Phone feels warm near the battery compartment on the first few charges

A new Li-ion cell starts with slightly higher internal impedance than a cell that has been cycled. The charge IC compensates by running at a higher voltage differential, which dissipates as heat in the battery compartment. This is normal during the first two to three charge cycles and reduces as impedance settles. If warmth persists beyond three cycles or the phone becomes hot to the touch, check that the battery contacts are fully seated and free of debris.