SoftBank P-10A Compatible Battery 3.7V 700mAh Li-ion

SoftBank P-10A / P-09A Series — 3.7V Li-ion Replacement Battery (P19 / AAP29235)

This is a 3.7V 700mAh Li-ion cell built to fit the SoftBank P-10A, P-09A, P-08A, P-07A, and three additional compatible models. It replaces the original OEM cell when the existing battery no longer holds a usable charge or fails to power on. Capacity figures come from product data — 700mAh, 2.59Wh.

• P-07A through P-10A platform compatibility: These four SoftBank handset generations share the same cell footprint at 45.20 × 37.75 × 4.21mm, the same 3.7V nominal voltage rail, and the same connector pinout — which is why one cell works across the range without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the bench. The BMS accepted charge current correctly, held voltage above the low-battery cutoff threshold under simulated screen and modem load, and released cleanly into deep-discharge recovery from below 3.0V.
• Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

The phone's fuel gauge IC was calibrated to the old cell's internal resistance profile. A new cell has a different voltage-versus-capacity curve, so the gauge reads remaining charge inaccurately. Under brief high-draw spikes — mobile data, screen brightness, GPS — the actual cell voltage drops below the system cutoff faster than the gauge predicts. The phone shuts down even though the reported percentage looks safe. One full discharge cycle, draining to automatic shutdown then charging to 100% without interruption, resets the coulomb counter and resolves this.

Phone reporting wrong battery percentage after the cell swap

After installing a new cell, the fuel gauge IC still holds the lookup table it built against the old degraded cell. Percentage readings can jump erratically or plateau for long periods before dropping sharply. This is not a fault with the replacement cell — it is a calibration lag in the gauge IC. Run two full discharge-charge cycles without interruption, and the coulomb counter rebuilds its mapping against the new cell. Percentage reporting stabilises by the end of the second cycle, typically settling within a few percent of actual remaining charge at the 3.7V nominal point.