LG Q8 2018 BL-T37 Replacement Battery 3.85V 3300mAh

LG Q8 2018 — 3.85V Li-Polymer Replacement Battery (BL-T37)

This is a 3300mAh (12.71Wh) 3.85V lithium-polymer cell replacement for the LG Q8 2018 smartphone. It fits the Q815L, Q815S, and Q8 2018 TD-LTE variants along with 39 additional regional models. OEM part numbers BL-T37 and EAC63958201 both cross-reference to this cell.

• Q8 2018 model family fit: LG's Q8 2018 lineup shares the same battery bay dimensions, connector pinout, and BMS handshake protocol across its regional variants. The 90.74 × 41.28 × 4.30mm cell matches the original cavity precisely, and the BMS communicates correctly with the Q8 charge IC on all affected models.
• Bench tested on actual hardware: We cycled this cell on a Q815S unit and monitored BMS communication, charge acceptance, and cutoff voltage. The cell reached full charge termination cleanly and the protection circuit tripped correctly at low-voltage threshold during a controlled deep-discharge test.
• Fuel gauge recalibration on first use: After installation, disable fast charging and run one complete discharge-to-charge cycle at standard current. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current fast charging pushes load into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on a replacement cell in the Q8 2018

This is a voltage cliff issue, not a capacity problem. When the modem transmits or the display runs at full brightness, current draw spikes sharply. If the fuel gauge IC is still calibrated to the old cell's discharge curve, it misreads the state of charge. The new cell's voltage drops below the shutdown threshold under that load spike before the reported percentage reaches zero. One full discharge-charge cycle at standard current lets the coulomb counter recalibrate and eliminates most of these early shutdowns.

USB fast charge not triggering after battery replacement on the Q8 2018

On the first charge cycle after a cell swap, the Q8's charge IC sometimes fails to negotiate the proprietary fast-charge handshake with the new BMS. The phone charges slowly or shows only standard 5V input even on a compatible fast charger. Disconnect the charger, allow the phone to power down fully, then reconnect — the charge IC re-initiates the handshake from a cold state. If fast charge still does not trigger, complete one full standard-current cycle first; the BMS accepts the fast-charge protocol reliably from the second cycle onward.