BST-10 Sony Ericsson R380 Replacement Battery 3.7V 1150mAh

Sony Ericsson R380 — 3.7V Li-ion Replacement Battery (BST-10)

The BST-10 is a 3.7V, 1150mAh Li-ion cell that fits the Sony Ericsson R380 smartphone. The R380 is an early-2000s touchscreen flip device, and original BST-10 cells have had decades to degrade. This replacement restores the cell to full rated capacity.

• R380 platform fit: The R380 uses a single-cell Li-ion pack with a three-contact connector carrying voltage, ground, and a thermistor line. The BST-10 form factor and contact pitch match the R380 battery bay without modification. No third-party BMS handshake is required — the R380 charge circuit reads cell voltage and thermistor resistance directly.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a controlled bench load, monitoring cutoff voltage at both ends. The BMS held low-side cutoff at approximately 3.0V and topped out at 4.2V, consistent with standard single-cell Li-ion spec. Capacity measured within 5% of the 1150mAh rated figure.
• Fuel gauge recalibration on first install: After fitting the BST-10, run the R380 from 100% down to automatic cutoff before recharging. The R380's fuel gauge IC learned the old cell's discharge curve over years of use — one full discharge-charge cycle resets that reference to the new cell and corrects percentage reporting.

Why the R380 shuts down at 20–30% after a cell swap

The R380's fuel gauge IC holds a discharge curve calibrated to the original cell. A new cell has a different internal resistance profile, so the IC misreads remaining capacity. Under screen or modem load, the phone hits a voltage point the IC interprets as empty — even though charge remains. One complete discharge-charge cycle rewrites the reference curve. After that cycle, shutdown behaviour at low percentages typically resolves.

R380 not powering on after the battery sat in storage

Li-ion cells self-discharge in storage. If the BST-10 dropped below roughly 2.5V per cell before installation, the protection circuit locks out charging to prevent damage to the degraded cell. The R380 will show no response at the power button. Connect the phone to a charger and leave it for 15–30 minutes without pressing anything — the charge IC delivers a low trickle current to bring the cell above the BMS recovery threshold before switching to normal charge mode. Once the LED indicator activates, the cell has cleared the lockout.