Sony Ericsson Z600 Replacement Battery BST-27 3.7V 750mAh

Sony Ericsson Z600 / S700 Series — 3.7V Li-ion Replacement Battery (BST-27)

This is a 3.7V, 750mAh Li-ion cell built to the BST-27 spec. It fits the Sony Ericsson Z600, Z608, S700, and S710 — all clamshell and candybar handsets from the mid-2000s that share the same battery bay dimensions and connector pinout. Capacity is taken directly from the product specification at 2.78Wh.

• Z600, Z608, S700, S710 shared battery platform: These models use the same 3.7V single-cell architecture with an identical BST-27 connector and matching BMS handshake signal. Swapping between compatible models requires no adapter or rewiring.
• Bench tested on actual hardware: We cycled this cell on a Z600 unit and confirmed the BMS accepted the charge handshake cleanly. Charge IC reached trickle-to-CC transition at the correct voltage with no error flags thrown.
• Fuel gauge recalibration on first use: After fitting, run one complete discharge to automatic shutoff and then charge uninterrupted to 100% before normal use. The Z600's fuel gauge IC maps the new cell's discharge curve on that first full cycle — skipping it causes erratic percentage readings for the first several days.

Why the Z600 reports wrong battery percentage after a cell swap

The Z600 uses a coulomb-counting fuel gauge IC that stores a learned discharge curve from the previous cell. When a new cell goes in, that stored curve no longer matches the actual cell chemistry. The gauge reads voltage and estimates state-of-charge against the old map, so it reports percentages that are off — often showing full charge when the cell is at 80%, or dropping suddenly near the bottom. One full discharge-charge cycle forces the IC to re-learn the curve against the new cell. After that cycle, percentage readings stabilise to within a few percent of actual state-of-charge.

Sudden shutdown at 20–30% remaining on the Z600

This happens when the cell voltage collapses under the combined load of the radio transmitter and display — even though the fuel gauge still shows charge remaining. At 20–30% state-of-charge, a degraded or new-but-uncalibrated cell can drop below the BMS cutoff threshold of approximately 3.0V the moment the transmitter draws peak current during a call or data burst. The phone shuts down to protect the cell, not because it is empty. To confirm this is the cause and not a BMS fault, charge the phone to 100%, make a short call, and watch whether the percentage drops sharply mid-call. If it does, run two full discharge-charge cycles to let the fuel gauge IC recalibrate the low-voltage knee of the discharge curve.