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BQ Aquaris M5.5 Replacement Battery 3.8V 3400mAh 3620

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From $25.99 USD $31.99
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Fits BQ Aquaris M5.5 smartphone, replaces OEM part number 3620.
Rated 3.8V and 3400mAh capacity; delivers the energy spec required for full system operation on this device.
Connector and internal contacts match the M5.5 battery slot; physical dimensions are 82.40 x 66.40 x 4.00 mm.
We bench-tested the new cell under modem and display load; BMS accepted charge current without fault and held voltage stable across the operating range.
On first use after installation, disable fast charging for one complete discharge-charge cycle so the fuel gauge IC recalibrates against the new cell curve before high-current charging resumes.
Delivery time

This product ships directly from our Manufacturer’s Warehouse and is usually delivered within 5 – 8 business days to your doorstep.

Discount: As a thank you for your patience, enjoy 5% off on your order
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Battery Care Tips

🔹 Getting Started

Charge your new battery fully before you use it for the first time. Over the next few charge cycles, run your device down to around 20% before you recharge—this helps the battery perform its best. After that, charge whenever you need to.

🔹 Keep It Healthy

Avoid letting your battery completely drain or staying plugged in constantly. Both extremes wear it out faster. Store the battery in a cool, dry place when you're not using it, since heat damages batteries quickly.

Delivery and Shipping

🔹 Most orders ship the next day, and we use FedEx, UPS, Purolator and other carriers to get them to you. Lithium batteries have to ship by ground only, not air or USPS. Make sure your address is right before you order, because if we have to send it back, you pay for shipping again.

Disclaimer

⚠️ Disclaimer: All product names, trademarks, and registered trademarks belong to their respective owners.

🔹 We use these names, brands, or model numbers only for identification and compatibility purposes.

Voltage

3.8V

Amp

3400mAh

BQ Aquaris M5.5 — 3.8V Li-Polymer Replacement Battery (3620)

This is a 3.8V, 3400mAh Li-Polymer cell for the BQ Aquaris M5.5 smartphone, cross-referenced to OEM part number 3620. It fits the internal battery bay of the M5.5 directly. If your phone shuts down unexpectedly, won't hold charge, or fails to power on, this cell addresses those fault conditions.

  • Aquaris M5.5 fitment: The M5.5 uses a fixed connector orientation and a BMS that negotiates directly with the phone's charge IC. This cell matches the connector pinout, the physical envelope (82.40 × 66.40 × 4.00 mm), and the voltage rail the board expects.
  • Bench tested on actual hardware: We ran charge-discharge cycles through the BMS and confirmed the protection circuit triggers correctly at low-voltage cutoff. The fuel gauge IC accepted the cell without throwing a fault flag after a full calibration cycle.
  • Fuel gauge recalibration after swap: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging is applied to an uncalibrated cell.

Why the Aquaris M5.5 reports wrong battery percentage after a cell swap

The M5.5 uses a coulomb counter that builds its fuel map against the original cell's impedance and discharge curve. When you install a new cell, the counter still references the old curve, so the percentage readout drifts — often showing full charge until the voltage drops suddenly. One complete slow-charge cycle forces the IC to re-learn the new cell's characteristics. After that cycle, percentage accuracy stabilises and the readout tracks the actual state of charge correctly.

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

This happens when the modem or display draws a peak current the cell can't sustain at low state-of-charge, causing the terminal voltage to sag below the BMS cutoff threshold — even though the reported percentage still looks safe. The fuel gauge hasn't recalibrated yet, so it's reporting a percentage that doesn't match the real voltage. Run one full discharge down to automatic shutdown, then charge uninterrupted to 100%. After that cycle, the coulomb counter anchors its low-end threshold correctly and the early shutdowns stop.

Compatible Models

Aquaris M5.5

Replaces Part Numbers

3620

Technical Specifications

Voltage3.8V
Amp Hours3400mAh
Capacity3400mAh
Rate12.92Wh
Net Weight52g /1.83 oz
Gross Weight87g /3.07 oz
Approximate Weight87g /3.07 oz
Dimension 82.40 x 66.40 x 4.00 mm

Product Highlights

  • Brand: BQ
  • Manufacturer: CS
  • Series: Standard
  • Color: Black
  • Product Type: Li-Polymer
  • Battery Type: Li-Polymer
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Aquaris M5.5 won't turn on at all after the replacement battery sat in a drawer for a few months — is it dead?

Likely not dead, but the cell discharged below the BMS lockout threshold, which sits around 2.5V per cell. At that voltage, the BMS cuts output to protect the cell and the phone won't respond to the power button. Connect the phone to a wall charger — not a PC USB port — and leave it for 20–30 minutes before attempting to power on. If the charge IC can trickle current into the cell past the lockout threshold, the BMS re-initialises and the phone boots normally.

Fast charging stopped working the first time I plugged in after fitting this battery — the phone just charges slowly now.

On the first cycle after a cell swap, the charge IC can reject the fast-charge handshake because the BMS presents higher impedance on a fresh cell than the IC's profile expects. This is normal behaviour, not a fault. Complete one full slow charge to 100%, then discharge to automatic shutdown, and plug in again. After that calibration cycle, the fast-charge protocol negotiates correctly and charging speed returns to normal.

The battery percentage on my M5.5 keeps jumping — it'll show 45%, then suddenly skip to 60% or drop to 30% within minutes.

Erratic percentage jumps are a fuel gauge IC recalibration issue, not a defective cell. The coulomb counter inherited calibration data from the old cell and hasn't mapped the new cell's discharge curve yet. Let the phone discharge fully until it shuts itself off, then charge in one uninterrupted session to 100% without using the phone. After that single full cycle, the IC resets its reference points and the percentage readings stabilise.

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