Hagenuk E20 Replacement Battery PHBA-309 3.7V 600mAh

Hagenuk E20 — 3.7V Li-ion Replacement Battery (PHBA-309)

This is a 3.7V, 600mAh Li-ion replacement battery for the Hagenuk E20 mobile phone. It replaces OEM part PHBA-309 when the original cell no longer holds a charge or has degraded to the point of causing shutdowns. Voltage and capacity match the original spec exactly.

• Hagenuk E20 fitment: The E20 uses a compact 41.54 x 41.54 x 4.47mm cell with a low 600mAh draw profile suited to the phone's basic modem and display stack. The connector and BMS communication protocol are matched to the original charge IC on the E20 board.
• Bench tested on actual hardware: We cycled this cell through the E20's charge IC and confirmed BMS handshake, charge termination at 4.2V, and stable voltage delivery under combined screen and modem load. No false full-charge cutoff was observed.
• Fuel gauge recalibration on first use: On first installation, disable fast charging if your charger supports it, then run one full discharge down to automatic shutoff before charging completely to 100%. This gives the fuel gauge IC a clean reference curve against the new cell before it starts tracking capacity under normal use.

Sudden shutdown at 20–30% on the Hagenuk E20 after a cell swap

This is a voltage cliff problem, not a capacity problem. The E20's fuel gauge IC was calibrated to the discharge curve of the original cell. When the phone's modem or display pulls current at the 20–30% mark, the new cell's voltage can drop below the system cutoff threshold before the percentage display reaches zero. The fuel gauge doesn't know this yet — it's still reading against the old curve. One full discharge-to-shutdown followed by a full charge to 100% resets the coulomb counter and maps it to the new cell's actual curve.

E20 showing erratic percentage jumps after replacement battery installed

Percentage jumping — say, from 54% down to 31% in minutes, or spiking back up when the load drops — is the fuel gauge IC actively recalibrating against an unfamiliar cell. It hasn't completed enough discharge cycles to build an accurate model of the new cell's voltage-to-capacity relationship. This is normal in the first one to three cycles after a cell swap. Run two full discharge-to-shutoff and charge-to-100% cycles and the reported percentage will stabilise.