Cyrus CM15 Replacement Battery CYR10015 3.7V 1700mAh

Cyrus CM15 — 3.7V Li-ion Replacement Battery (CYR10015)

This is a 3.7V, 1700mAh Li-ion cell for the Cyrus CM15 smartphone. It replaces the original battery when capacity has faded or the cell has failed outright. Voltage and connector match the CM15 board — no modification needed.

• CM15 platform fit: The CM15 uses a single-cell 3.7V Li-ion pack with a specific connector orientation and BMS pin-out. This cell matches that layout. The protection circuit handles overvoltage, undervoltage, and short-circuit cutoff the same way the OEM cell does.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on the CM15 board. The BMS handshake completed without error flags, and the charge IC accepted the cell without triggering a fault state.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve accurately before high-current charging is applied to an uncalibrated cell.

Why the CM15 reports wrong battery percentage after a cell swap

The CM15 uses a coulomb counter that builds its reference model from the previous cell's charge history. When a new cell goes in, that reference is stale. The phone reads state-of-charge against the old curve, so displayed percentage drifts from actual capacity. One full discharge to auto-shutdown followed by an uninterrupted charge to 100% resets the counter against the new cell's actual characteristics.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC hasn't recalibrated yet. At 20–30% indicated charge, the cell voltage drops below the load threshold under modem or screen demand — the phone cuts power before the display catches up. The protection circuit trips at approximately 3.0V under load. Run one full cycle without fast charge and the gauge will track the real voltage floor correctly from the second cycle onward.