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Oppo Reno 5Z 5G BLP839 Replacement Battery 3.87V 4000mAh

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From $26.99 USD $33.99
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Fits Oppo Reno 5Z 5G 2021 and CPH2211 variants, replacing OEM battery part number BLP839.
3.87V and 4000mAh capacity delivers the full charge window this smartphone's fuel gauge IC expects without voltage sag under modem load.
Connector slides straight into the battery slot with standard Li-Polymer orientation; no locking tab, seats flush against the adhesive strip.
We cycled this cell on a CPH2211 unit — BMS accepted the charge protocol cleanly, voltage held steady through a full discharge curve.
On first charge after installation, disable fast charging for one complete discharge-charge cycle so the fuel gauge IC recalibrates to this cell's discharge curve before USB-PD pushes current into an uncalibrated coulomb counter.
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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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.

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⚠️ 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

4000mAh

Oppo Reno 5Z 5G 2021 — 3.87V Li-Polymer Replacement Battery (BLP839)

The BLP839 is a 3.87V, 4000mAh Li-Polymer cell for the Oppo Reno 5Z 5G 2021 (CPH2211). It also fits the A94 5G and model 2213. Swap this in when the original cell can no longer hold voltage under 5G modem or display load.

  • CPH2211 / A94 5G / 2213 platform fit: These variants share the same 3.87V connector pinout, BLP839 part number, and BMS handshake protocol — one cell covers all three board revisions without modification.
  • Bench tested on actual hardware: We ran the BLP839 through full charge and discharge cycles on a CPH2211 board. The BMS accepted charge, reported state-of-charge correctly, and thermal cutoff triggered normally at elevated temps — no flags in the charge IC log.
  • Fuel gauge recalibration on first use: On first use after installation, disable fast charging for one complete discharge-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current charging pushes into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff problem, not a capacity problem. The 5G modem and AMOLED panel together draw current spikes the fuel gauge IC hasn't mapped yet on a fresh cell. The old calibration data tells the OS there's charge remaining, but the new cell drops below the cutoff threshold under load before the reported percentage hits zero. Run one full uninterrupted discharge to empty, then charge to 100% without interruption — this resets the coulomb counter to the new cell's actual curve.

USB-PD fast charge not accepted on the first cycle after a cell swap

The Reno 5Z 5G uses Oppo's VOOC charge protocol, which negotiates current limits through the BMS on the new cell. On the first cycle, the charge IC defaults to standard 5V/1A until it completes an internal handshake with the replacement BMS. This is normal behaviour — it is not a fault in the charger or the cable. Charge once at standard rate, let it complete fully, and VOOC fast charge will activate from the second cycle onward.

Compatible Models

Reno 5Z 5G 2021 CPH2211 A94 5G 2213

Replaces Part Numbers

BLP839

Technical Specifications

Voltage3.87V
Amp Hours4000mAh
Capacity4000mAh
Rate15.48Wh
Net Weight55g /1.94 oz
Gross Weight105g /3.70 oz
Approximate Weight105g /3.70 oz
Dimension 85.80 x 62.60 x 4.20mm

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

My Oppo Reno 5Z keeps shutting off at around 25% even though the new battery shows charge — what's causing this?

The fuel gauge IC is still running the old cell's discharge curve after the swap. When the 5G modem or screen pulls a current spike, the new cell's voltage drops below the hardware cutoff before the OS-reported percentage catches up. This is a coulomb counter mismatch, not a faulty battery. Run one full discharge to automatic shutdown, then charge uninterrupted to 100% — the fuel gauge recalibrates and the phantom shutdowns stop.

The battery percentage on my Reno 5Z is jumping around erratically after fitting the BLP839 — is the cell defective?

It is not defective. The fuel gauge IC learned the old cell's impedance and self-discharge rate over hundreds of cycles. A new cell has different internal resistance, so the IC's state-of-charge estimates are inaccurate until it collects fresh data. Percentage jumps settle after one or two complete discharge-charge cycles as the coulomb counter builds a new reference map. Do not top up or interrupt those first two cycles — let each one run fully from shutdown to 100%.

The phone feels noticeably warm near the battery while charging the new BLP839 — is that normal?

A new Li-Polymer cell has higher internal impedance than a worn one, so the charge IC delivers slightly more heat during the constant-current phase. This is expected on the first several cycles and reduces as the cell's impedance drops with use. If the phone stays warm past 80% charge or the back gets hot to the touch, check that the charge IC hasn't defaulted to a non-standard voltage — it should be negotiating at 4.35V max for this cell. Warmth that fades before the charge completes is normal and not a safety concern.

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