EBA-110 BenQ-Siemens AL21 Compatible Battery 3.7V 700mAh

BenQ-Siemens AL21 / AL26 — 3.7V Li-ion Replacement Battery (EBA-110)

This is a 3.7V 700mAh Li-ion cell matching OEM part number EBA-110, built to fit the BenQ-Siemens AL21 and AL26 compact mobile phones. Both models share the same battery bay dimensions and connector, so one cell covers both. Capacity is rated at 700mAh / 2.59Wh, matching the original specification.

• AL21 and AL26 shared platform: Both phones run off the same 3.7V single-cell architecture with an identical 44 × 36 × 6mm battery envelope and shared connector pinout. The BMS on each handset uses the same voltage thresholds, so one replacement cell works across both without any firmware conflict.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a BMS-monitored rig. The protection circuit tripped correctly at the low-voltage cutoff and accepted a full CC/CV charge cycle without thermal anomaly or premature cutoff.
• Fuel gauge recalibration on first use: After fitting this cell, run one complete discharge down to automatic shutdown, then charge uninterrupted to 100% before using the phone normally. The AL21's fuel gauge IC was calibrated to the worn original cell — skipping this step causes the percentage counter to read against the wrong discharge curve from day one.

Why the AL21 reports wrong battery percentage after a cell swap

The AL21 uses a coulomb-counting fuel gauge IC that builds its state-of-charge model from previous discharge cycles. When you replace the cell, the IC still holds the old cell's discharge profile in memory. It maps current draw against that stale curve, so the percentage shown on screen drifts away from actual charge state almost immediately. One full discharge-to-shutdown followed by a complete uninterrupted charge forces the IC to rewrite its reference curve against the new cell's actual capacity.

Sudden shutdown at 20–30% on the replacement cell

This happens when the fuel gauge IC has not yet recalibrated and the phone hits a voltage cliff before the displayed percentage reaches zero. The screen backlight and radio combined pull enough current to drop cell voltage below the BMS cutoff threshold while the counter still shows charge remaining. It is not a faulty cell — it is a calibration gap. Run the recalibration cycle described above, and the shutdowns stop once the IC has a full discharge curve for this cell. After calibration, the cutoff should align at or below 3.4V under load.