Lenovo BL210 S820 Replacement Battery 3.7V 2000mAh

Lenovo S820 / A770E Series — 3.7V Li-ion Replacement Battery (BL210)

This is a 3.7V, 2000mAh Li-ion replacement cell for the Lenovo S820, S820e, A750e, and A770E smartphones. It slots into the original battery bay and connects via the existing ribbon contact. Use the capacity figure above — 2000mAh — as the reference spec for this cell.

• S820 and A-series compatibility: The S820, S820e, A750e, and A770E all share the same battery bay dimensions, contact pitch, and 3.7V supply rail. The BL210 part number covers this group because the BMS handshake and connector pinout are identical across these models.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a monitored rig. The BMS held charge cutoff at 4.2V and triggered low-voltage protection at 3.0V. No thermal spike was recorded during the first full charge.
• Fuel gauge recalibration on first use: After fitting this cell, disable fast charging and run one complete discharge down to automatic shutdown, then charge to 100% uninterrupted. This gives the fuel gauge IC one clean reference cycle against the new cell's discharge curve before fast charge current is applied.

Why the S820 reports wrong battery percentage after a cell swap

The S820 uses a coulomb-counting fuel gauge IC that builds its percentage model against the previous cell's charge curve. When a new cell goes in, that stored curve no longer matches. The gauge reads an offset voltage and maps it to the wrong state-of-charge point. One full discharge-to-shutdown and uninterrupted recharge to 100% resets the reference table. After that cycle, percentage reporting stabilises.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the modem or display triggers a load spike and the cell voltage drops below the BMS cutoff threshold — even though the gauge still shows charge remaining. It is a voltage-cliff issue, not a capacity issue. The BMS sees the instantaneous sag past 3.0V and shuts the device down as a protection measure. Run the fuel gauge recalibration cycle first; if shutdowns continue past that point, check that the battery contact pins on the motherboard are clean and making full contact.