BLU Neo 3.5 C525145130L Replacement Battery 3.7V 1200mAh

BLU Neo 3.5 / S310L / S370 — 3.7V Li-ion Replacement Battery (C525145130L)

This is a 3.7V, 1200mAh Li-ion cell that replaces the original battery in the BLU Neo 3.5 and compatible S-series models. It fits the Neo 3.5, S310L, S310U, and S370, among others. OEM part numbers C525145130L and C535143130T both cross to this cell.

• Neo 3.5 and S-series shared battery platform: These models use the same 52.23 × 50.93 × 4.50 mm form factor and 3.7V nominal rail. The connector pinout and BMS communication protocol are identical across the group, so one cell covers the full compatibility list.
• Bench tested on actual hardware: We cycled this cell through full charge and discharge on a Neo 3.5 unit. The BMS handshake completed cleanly, charge IC accepted the cell without fault flags, and the fuel gauge IC tracked state-of-charge across the full curve without resets.
• First-cycle fuel gauge calibration: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle before enabling it again. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state.

Why the Neo 3.5 reports wrong battery percentage after a cell swap

The fuel gauge IC on the Neo 3.5 stores a learned discharge curve from the original cell. When a new cell goes in, that stored curve no longer matches the actual cell chemistry, so percentage readings drift — often reading higher or lower than real remaining capacity. The fix is one full discharge cycle from 100% down to automatic shutdown, then a full uninterrupted charge to 100%. After that cycle, the coulomb counter resets its baseline to the new cell and percentage accuracy stabilises.

Sudden shutdown at 20–30% on the replacement cell

This happens when the modem or display fires a high-current draw spike and the cell voltage drops sharply below the BMS cutoff threshold — even though the percentage display still shows charge remaining. It is a voltage cliff issue, not a capacity issue: the fuel gauge IC reported percentage based on an old curve while the actual cell voltage collapsed under load. Run one full calibration cycle as described above. If shutdowns persist below 3.2V under load after calibration, the cell has developed high internal impedance and needs replacement.