LG K510 Replacement Battery BL-T49 3.85V 3900mAh

LG K510 / K51S Series — 3.85V Li-Polymer Replacement Battery (BL-T49)

This is a 3900mAh Li-Polymer replacement battery for the LG K510, K51S, LM-K410BMW, and LM-K510BMW smartphones. It slots into the same battery bay as the original BL-T49. Voltage is 3.85V nominal, matching the charge IC and BMS thresholds LG set at the factory.

• K510 and K51S platform compatibility: These models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The BL-T49 footprint — 78.00 × 66.05 × 4.20mm — fits all four variants without modification to the housing or flex cable routing.
• Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a K510 unit. The BMS accepted the cell without fault codes, the charge IC stepped through trickle, bulk, and CV phases correctly, and the fuel gauge IC registered capacity within the expected range on the second cycle.
• First-cycle fast charge behaviour: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes current into an uncalibrated cell — reducing the chance of premature cutoff on early cycles.

Sudden shutdown at 20–30% on the K510 after a cell swap

The K510's fuel gauge IC calibrates its coulomb counter against the original cell's internal resistance curve. A new cell has different impedance characteristics, so the IC's state-of-charge model becomes inaccurate. Under modem load or screen-on draw, voltage drops faster than the IC predicts, and the phone hits the hardware voltage floor before the displayed percentage reaches zero. One full discharge-charge cycle without fast charging lets the IC relearn the curve. After that cycle, the percentage reading stabilises and shutdowns at false-high percentages stop.

Phone warm near the battery bay on the first few charges

A fresh Li-Polymer cell starts with slightly higher internal impedance than a broken-in one. The charge IC dissipates more energy as heat during the bulk charge phase while impedance is elevated. This is normal on the first two or three charge cycles and resolves as the cell cycles in. If the device stays warm past the fifth charge or gets hot enough to be uncomfortable to hold, that points to a charge IC fault on the board — not the cell itself. Check that the battery connector is fully seated before drawing that conclusion.