Simvalley XL-915 Replacement Battery 3.7V 750mAh Li-ion

Simvalley XL-915 — 3.7V Li-ion Replacement Battery

This 3.7V, 750mAh Li-ion battery replaces the original cell in the Simvalley XL-915 smartphone. It fits the XL-915 and XL915 variants and restores power to units where the original cell has degraded or failed. Capacity figure is 2.78Wh as rated by the manufacturer.

• XL-915 and XL915 fitment: Both model designations use the same physical cell format — 53.00 x 33.90 x 5.70mm — with the same connector pin-out and BMS handshake voltage. One cell covers both.
• Bench tested on actual hardware: We cycled this cell through charge, standby, and active load on the XL-915 board. The BMS accepted the cell without fault flags and the charge IC reached termination voltage cleanly at 4.2V.
• First-cycle calibration on the XL-915: On first use after installation, disable fast charging if your firmware supports it. Run one full discharge-to-charge cycle at standard rate. This gives the fuel gauge IC a complete discharge curve to map against the new cell before high-current charging begins on an uncalibrated counter.

Why the XL-915 reports the wrong battery percentage after a cell swap

The XL-915 uses a fuel gauge IC that tracks charge state by counting coulombs against a stored discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual cell characteristics. The gauge reads as though it knows where it is on the curve — but it doesn't. One full discharge from 100% down to automatic shutdown, followed by a complete charge, forces the IC to rewrite its reference curve against the new cell. After that cycle, percentage readout tracks accurately.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or screen draws a short high-current burst and the cell voltage drops below the BMS cutoff threshold faster than the fuel gauge can track. The gauge still shows 20–30% remaining, but the actual cell voltage has sagged below 3.2V under load. It is not a faulty battery — it is an uncalibrated gauge reading a new cell with a different internal resistance profile. Run the full discharge-charge calibration cycle described above and confirm the phone reads 0% at automatic shutdown before the next charge.