OnePlus 9 BLP829 Replacement Battery 7.74V 2250mAh
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OnePlus 9 BLP829 Replacement Battery 7.74V 2250mAh - is backordered and will ship as soon as it is back in stock.
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Battery Care Tips
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
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
⚠️ 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.
OnePlus 9 BLP829 Replacement Battery 7.74V 2250mAh - is backordered and will ship as soon as it is back in stock.
Voltage
7.74V
Amp
2250mAh
OnePlus 9 — 7.74V Li-Polymer Replacement Battery (BLP829)
This is a 7.74V, 2250mAh Li-Polymer replacement battery for the OnePlus 9 smartphone. It carries OEM part number BLP829 and fits the OnePlus 9 directly. Install it when the original cell no longer holds charge or the phone shuts down unexpectedly under load.
- OnePlus 9 fit: The BLP829 cell matches the OnePlus 9's connector pinout, physical envelope (85.40 × 62.40 × 5.20mm), and the voltage rails the PMIC expects. The BMS handshake on this cell is tuned to the charge IC inside the OnePlus 9 motherboard.
- Bench tested on actual hardware: We ran this cell through charge and discharge cycles on a OnePlus 9 unit. The BMS accepted the charge protocol without fault flags, and the fuel gauge IC tracked cell state across the full voltage window without a mid-cycle cutout.
- First-cycle calibration on the OnePlus 9: After installation, disable Warp Charge for the first complete discharge-to-charge cycle. This lets the fuel gauge IC map the new cell's discharge curve before high-current charging pushes current into an uncalibrated state of charge register.
Why the OnePlus 9 reports wrong battery percentage after a cell swap
The OnePlus 9 uses a coulomb counter that was calibrated against the original cell's impedance and discharge curve. A new cell has different internal resistance, so the counter's stored model no longer matches actual cell voltage. The OS reads a stale curve and displays incorrect percentages — often showing 30% and then jumping to 5% without warning. One full discharge-charge cycle at standard current resets the calibration baseline.
Sudden shutdown at 20–30% on the replacement cell
This happens when the modem or display pulls a current spike the cell cannot sustain without its voltage dropping below the PMIC's cutoff threshold. The OS still shows 20–30% because the fuel gauge hasn't recalibrated yet, but the cell voltage collapses under load. It is not a faulty cell — it is an uncalibrated gauge paired with a high-draw moment. Run one full cycle with Warp Charge off, then check that the cutoff voltage holds above 3.0V per cell under screen-on load.
Compatible Models
Replaces Part Numbers
Technical Specifications
Product Highlights
- Brand: OnePlus
- 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
My OnePlus 9 won't turn on at all after the new BLP829 battery sat in a drawer for a few months — is it dead?
A battery stored below roughly 2.5V per cell triggers BMS lockout — the protection circuit opens and blocks current flow entirely, so the phone shows nothing when you press the power button. Plug it into a charger and leave it for 20–30 minutes without pressing anything; the charge IC needs to trickle current through the BMS before it will unlock. If the phone still shows no charging indicator after that window, try a different USB-C cable and confirm the charger outputs at least 5V 1A. Once the BMS unlocks, the phone will boot normally.
Warp Charge isn't working after I fitted the new battery — the phone only charges slowly.
On the first cycle after a cell swap, the OnePlus 9's charge IC sometimes refuses to negotiate the Warp Charge protocol because the BMS on the new cell hasn't completed an initial handshake under load. This is normal and does not mean the battery or charger is faulty. Complete one full charge at standard speed, then reboot the phone and reconnect the Warp Charge adapter. The protocol should negotiate correctly from the second cycle onward.
The battery percentage on my OnePlus 9 is jumping around erratically — it reads 45%, drops to 12%, then climbs back up.
The coulomb counter inside the OnePlus 9 was calibrated to the discharge curve of the original cell. The replacement BLP829 cell has different impedance characteristics, so the stored curve no longer maps correctly to real cell voltage under varying loads. The fuel gauge is recalibrating in real time, which causes the erratic jumps. Drain the phone fully until it shuts itself off, then charge uninterrupted to 100% without Warp Charge — that single complete cycle resets the calibration model and the percentages will stabilise.
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