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BLP865 Oppo K9 Pro Replacement Battery 3.87V 4400mAh

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From $31.99 USD $39.99
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Fits Oppo K9 Pro, K9 Pro 5G, and PEYM00 variants; replaces OEM part number BLP865.
3.87V and 4400mAh lithium-polymer cell restores full charge capacity on phones reporting 80–90% max.
Connector orientation matches original; locking tab slides into the battery door slot without force.
We bench-tested this cell in a K9 Pro unit; the fuel gauge IC accepted the new BMS signature after power-on.
On first use after installation, disable fast charging for one complete discharge-charge cycle so the coulomb counter recalibrates against the new cell curve before USB-PD pushes current into an uncalibrated sensor.
Delivery time

This product ships directly from our Manufacturer's Warehouse and is usually delivered within 7 – 10 business days to your doorstep.

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Fresh Battery, Worth the Wait

To provide the highest-quality replacement battery, we ship this battery directly from the manufacturer rather than from aging warehouse inventory. This means delivery may take a little longer, but it helps ensure you receive a fresh battery with better performance, a longer lifespan, and greater reliability.

Estimated delivery: 7–10 business days
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By continuing with your purchase, you acknowledge and agree to the estimated 7–10 business day delivery timeframe.
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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

3.87V

Amp

4400mAh

Oppo K9 Pro Series — 3.87V Li-Polymer Replacement Battery (BLP865)

The BLP865 is a 3.87V, 4400mAh (17.03Wh) lithium-polymer cell that fits the Oppo K9 Pro, K9 Pro 5G, K9 Pro 5G 2021 Standard Edition, and PEYM00. It replaces the original cell when capacity has dropped from repeated charge cycles or the battery no longer holds a usable charge. Swapping this cell restores the phone to factory power capacity without replacing the entire handset.

  • K9 Pro platform fit: The K9 Pro, K9 Pro 5G, and PEYM00 variants all share the same battery bay dimensions, flex connector pinout, and BMS handshake protocol — that is why one BLP865 cell covers all of them. Voltage rails and connector locking tabs are identical across the lineup.
  • Bench tested on actual hardware: We ran the BLP865 through charge-discharge cycles on K9 Pro hardware and logged BMS communication, cutoff thresholds, and charge IC handshake. The cell accepted VOOC fast charge correctly after the first full calibration cycle completed.
  • Fuel gauge recalibration on first use: On first use after installation, disable fast charging and run one complete discharge down to automatic shutdown, then charge to 100% uninterrupted. This lets the coulomb counter recalibrate against the new cell's discharge curve before high-current VOOC charging resumes.

Why the K9 Pro reports wrong battery percentage after a cell swap

The K9 Pro uses a coulomb counter tied to a fuel gauge IC that was calibrated against the original cell's specific discharge curve. When a new BLP865 goes in, that learned curve no longer matches the cell's actual voltage-to-capacity relationship. The gauge reads from stored reference data, not the new cell, so displayed percentages can jump or stall. One full discharge-to-shutdown followed by an uninterrupted charge to 100% forces the IC to rebuild its reference map against the replacement cell.

Sudden shutdown at 20–30% on the replacement BLP865

This happens when the fuel gauge IC is still running the old cell's voltage curve and the reported percentage does not reflect actual cell voltage. Under modem or display load, the real cell voltage drops below the 3.2V cutoff threshold before the reported percentage warns you. The phone shuts off to protect the cell even though the screen showed charge remaining. Run one full recalibration cycle first — discharge to auto-shutdown, then charge to 100% — and the shutdowns will stop once the gauge tracks the new cell correctly.

Compatible Models

K9 Pro K9 Pro 5G K9 Pro 5G 2021 Standard Edition PEYM00 K9 Pro 5G 2021 Premium Edition

Replaces Part Numbers

BLP865

Technical Specifications

Voltage3.87V
Amp Hours4400mAh
Capacity4400mAh
Rate17.03Wh
Net Weight60.5g /2.13 oz
Gross Weight110.5g /3.90 oz
Approximate Weight110.5g /3.90 oz
Dimension 85.50 x 62.40 x 4.60mm

Product Highlights

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

Frequently Asked Questions

VOOC fast charging isn't working after I replaced the battery — the phone is only slow charging now

The VOOC charge IC performs a handshake with the battery BMS on the first connection, and a freshly installed cell sometimes fails that handshake until the BMS has completed one full standard charge cycle. Plug in with the original VOOC adapter, let the phone charge slowly to 100% without interruption, then disconnect and restart the phone. On the next charge cycle, the VOOC protocol should be accepted normally.

The phone won't turn on at all after the replacement BLP865 sat in a drawer for a few months before installation

If the cell self-discharged below approximately 2.5V during storage, the BMS enters a lockout state to prevent charging a dangerously low lithium cell at full current. Plug into a VOOC-compatible charger and leave it connected for 20–30 minutes without attempting to power on — the BMS uses trickle current to recover the cell voltage to a safe level before allowing normal charging to begin. Once the charge indicator appears on screen, the BMS has exited lockout and normal charging will proceed.

The phone feels warm near the battery area during the first few charges with the new cell — is that normal?

A new high-impedance cell has slightly more internal resistance than a cell that has been through conditioning cycles, so the charge IC dissipates a little more heat during those first charges. This is temporary and should reduce noticeably after three to five complete charge cycles as internal resistance drops. If the phone becomes hot enough to be uncomfortable to hold, stop charging and check that the connector flex is fully seated — a partially connected cell forces the charge IC to work harder. After proper seating and a few cycles, warmth during charging should return to the same level as the original cell.

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