Yakumo Delta X GPS Replacement Battery 3.7V 1250mAh

Yakumo Delta X GPS — 3.7V Li-ion Replacement Battery

This is a 3.7V, 1250mAh Li-ion cell for the Yakumo Delta X GPS smartphone. It replaces a degraded or failed original battery. The cell measures 53.44 × 37.14 × 7.66mm and fits directly into the Delta X GPS battery bay.

• Delta X GPS platform fit: The Delta X GPS uses a single-cell 3.7V Li-ion pack with a connector and BMS handshake matched to Yakumo's charge IC. This cell meets those voltage and communication requirements.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge without fault flags, and the protection circuit triggered correctly at the low-voltage cutoff threshold.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one full discharge-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging begins on an uncalibrated cell.

Sudden shutdown at 20–30% on the Delta X GPS after a cell swap

This is a voltage cliff issue, not a capacity defect. The fuel gauge IC still references the old cell's discharge curve, so its percentage estimate drifts from the new cell's actual voltage. Under load — GPS active, modem transmitting, screen on — the new cell's voltage drops faster than the IC predicts. The phone's undervoltage protection shuts the device down before the displayed percentage reaches zero. Run one full uninterrupted discharge to empty, then charge to 100% without interruption, and the coulomb counter will re-anchor to the new cell.

Phone not powering on after the replacement cell sat in storage

Li-ion cells self-discharge during storage. If the cell voltage dropped below approximately 2.5V, the BMS will have entered lockout mode and will refuse to pass current to the device. The phone will show no response — no charge indicator, no boot. Connect to a wall charger rather than a PC port, which delivers steady 5V at higher current, and leave it for 20–30 minutes before attempting to power on. Once the BMS detects the cell recovering above its recovery threshold, it will release the lockout and normal charging will resume.