About this replacement
Samsung SGH-X708 — 3.7V Li-ion Replacement Battery
This is a 3.7V 850mAh Li-ion battery for the Samsung SGH-X708 candybar mobile phone. It replaces the original cell when the existing battery no longer holds a charge, swells, or fails to power the device. Dimensions are 62.00 × 36.70 × 8.42mm — confirm against your existing cell before fitting.
- SGH-X708 fit: The X708 uses a compact rectangular Li-ion cell at 3.7V nominal. This replacement matches that voltage rail and physical footprint so the battery door closes flush and the contact pins seat correctly.
- Bench tested on actual hardware: We cycled this cell through full discharge and charge sequences, confirming the BMS holds charge termination at the correct cutoff voltage and does not trip prematurely under typical phone load.
- Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge to 100% without interruption. The SGH-X708 fuel gauge IC needs this full cycle to map its coulomb counter to the new cell's discharge curve — skipping it causes the percentage indicator to jump or read incorrectly.
Sudden shutdown at 20–30% on the SGH-X708 after a cell swap
The X708's fuel gauge IC retains the discharge curve of the old cell after a swap. When the phone hits a load spike — a call connecting, backlight turning on — the new cell's actual voltage drops below the BMS cutoff threshold before the gauge reads zero. The phone shuts off while the display still shows charge remaining. One full discharge-to-shutdown followed by an uninterrupted charge to 100% resets the coulomb counter and eliminates this behaviour.
Phone feels warm near the battery during the first charge after replacement
A new high-impedance cell has slightly higher internal resistance than a broken-in cell. During the first charge cycle, the charge IC pushes current into that resistance, generating more heat than usual. This is normal for the first one or two cycles and reduces as the cell's internal resistance settles. If the back of the phone stays noticeably warm beyond the second full charge, check that the battery is seated flat with no contact between the cell and the chassis edge.