BLU J4 Replacement Battery 3.8V 2200mAh C835842220L

BLU J4 / J170 Series — 3.8V Li-Polymer Replacement Battery (C835842220L)

This 3.8V, 2200mAh lithium-polymer cell replaces the original C835842220L battery in the BLU J4, J170, and J170EQ smartphones. It fits the same physical cavity and connector as the factory cell. Capacity figure is 2200mAh / 8.36Wh — use that number, not anything printed on the old cell if it has faded.

• J4 / J170 / J170EQ fit: All three models share the same battery bay dimensions (83.15 × 58.00 × 4.20mm), the same 3.8V nominal rail, and the same connector pinout. One cell covers the whole lineup without any adapter or modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on the J170 platform. The BMS accepted charge handshake on the first connection, voltage held steady across the full discharge curve, and the protection circuit tripped cleanly at the low-voltage threshold with no false cutoff.
• First-cycle fuel gauge recalibration: After fitting this cell, disable fast charging in the device settings and run one complete discharge-to-charge cycle at standard rate. The fuel gauge IC on BLU J-series phones calibrates against the cell's discharge curve — skipping this step leaves the coulomb counter mismatched to the new cell and causes erratic percentage readings.

Sudden shutdown at 20–30% on the BLU J4 after a cell swap

This is a voltage cliff issue, not a faulty cell. The J4's modem and display together pull enough current to cause a brief voltage sag. If the fuel gauge IC is still calibrated to the old, worn cell's curve, it reports 25% when the actual state of charge is already near the BMS low-voltage cutoff. The phone shuts down because the cell voltage drops below 3.4V under load, even though the percentage shown looks safe. One full standard-rate discharge-charge cycle resets the coulomb counter to the new cell's actual curve and eliminates the premature cutoff.

Phone feels warm near the battery during the first few charges

A new lithium-polymer cell has higher internal impedance than a cell that has been through several cycles. The charge IC pushes current into that higher impedance, and some energy dissipates as heat during the first two or three charges. This is normal and reduces as the cell's impedance drops with cycling. If the phone stays warm past the fourth charge cycle, check that the back cover is seated flat — a lifted cover traps heat against the cell. Surface temperature should stabilise below 40°C by the third full charge.