Maas CB-28 Compatible Battery CP-228-EU 3.7V 1050mAh

Maas CP-228-EU — 3.7V Li-ion Replacement Battery (CB-28)

This is a 3.7V, 1050mAh Li-ion replacement battery for the Maas CP-228-EU smartphone. It replaces part number CB-28 when the original cell has degraded or failed. Capacity is 3.89Wh, matching the stock specification for this handset.

• CP-228-EU fit: The CB-28 cell is keyed to this handset's battery bay — connector pin-out, physical dimensions (53.16 × 33.77 × 5.34mm), and BMS communication match the original. No modification needed for installation.
• Bench tested on actual hardware: We ran the CB-28 replacement through full charge and discharge cycles on the CP-228-EU. The BMS handshake completed correctly, charge termination triggered at the expected cutoff voltage, and the protection circuit responded normally to discharge load.
• Fuel gauge recalibration after swap: On first use after installation, disable fast charging and run one complete discharge-to-charge cycle. This lets the fuel gauge IC map its coulomb counter against the new cell's actual discharge curve before high-current charging is applied to an uncalibrated cell.

Sudden shutdown at 20–30% on the CP-228-EU after a cell swap

This happens because the fuel gauge IC is still running the discharge curve from the old cell. When voltage drops under screen or modem load, the cell hits a voltage cliff that the IC did not predict — and the phone shuts off before the reported percentage reaches zero. The fix is one full uninterrupted discharge from 100% down to automatic shutdown, followed by a full charge. After that cycle the coulomb counter recalibrates to the new cell and percentage readings stabilise. Confirm the recalibration held by checking that the phone reaches 3.0V at shutdown rather than cutting off early at a higher reported figure.

CP-228-EU not powering on after the battery sat in storage

If a Li-ion cell drops below 2.5V per cell during storage, the BMS trips into lockout mode to prevent damage — the phone will not respond to the power button or show a charging indicator. Connect the phone to a wall charger (not a USB hub) and leave it undisturbed for 15–20 minutes. The charge IC trickle-charges the cell back above the BMS re-enable threshold, typically around 2.9–3.0V, at which point the BMS re-initialises and normal charging resumes. If the phone still shows no response after 30 minutes on a wall adapter, check the cable and adapter with a different device before ruling out the cell.