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Samsung Galaxy S21 Ultra Replacement Battery EB-BG998ABY 3.87V 4900mAh

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From $26.99 USD $33.99
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Fits Galaxy S21 Ultra and S21 Ultra 5G — replaces Samsung OEM part EB-BG998ABY.
3.87V Li-Polymer cell with 4900mAh capacity delivers sustained voltage under processor and display load.
Connector slides straight into battery slot with locking tab on the right side of the compartment.
We bench-tested this cell on a Galaxy S21 Ultra — fuel gauge IC accepted the new BMS handshake without faults.
On first use after installation, disable fast charging for one complete discharge-charge cycle to let the coulomb counter recalibrate against the new cell's discharge curve.
Delivery time

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

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

4900mAh

Samsung Galaxy S21 Ultra — 3.87V Li-Polymer Replacement Battery (EB-BG998ABY)

This is a 3.87V, 4900mAh Li-Polymer replacement battery for the Samsung Galaxy S21 Ultra and Galaxy S21 Ultra 5G. It fits SM-G998N, SM-G9980, and related variants where the original EB-BG998ABY has degraded or failed. Capacity is 18.96Wh — identical to the factory specification.

  • S21 Ultra and 5G variants: The SM-G998 series shares a single battery footprint, connector pinout, and BMS handshake across all regional builds. One cell fits the full lineup without adapter or modification.
  • Bench tested on actual hardware: We ran this cell on an SM-G998B through a full charge cycle, confirmed BMS communication with the charge IC, and verified the fuel gauge IC registered the correct capacity after one complete discharge pass.
  • First-cycle fast charge protocol: On first use after installation, disable fast charging and run one full discharge-to-charge cycle. This lets the fuel gauge IC recalibrate against the new cell's discharge curve before high-current fast charging pushes current into an uncalibrated cell.

Sudden shutdown at 20–30% on the replacement cell

This is a voltage cliff issue, not a capacity defect. When the modem, display, and processor draw peak current simultaneously, a freshly installed cell with an uncalibrated fuel gauge IC can drop below the BMS cutoff threshold before the percentage reading reflects it. The phone shuts down because actual cell voltage falls under load, even though the reported percentage looks safe. Run one full discharge cycle without fast charging — this lets the coulomb counter reset its baseline and the shutdowns stop.

Phone will not power on after the battery sat in storage

Li-Polymer cells self-discharge in storage. If a replacement cell has been sitting long enough, cell voltage can fall below 2.5V per cell — the point where the BMS locks out to prevent damage. The phone won't respond to the power button and may show nothing on screen. Connect to a wall charger via USB-C and leave it for 20–30 minutes before pressing power. Once the BMS sees voltage above the recovery threshold, it releases the lockout and charging resumes normally.

Compatible Models

Galaxy S21 Ultra Galaxy S21 Ultra 5G SM-G998N SM-G9980 SM-G998D SC-52B SGH-N748 SM-G998W SM-G998B/DS SM-G998V SM-G998U SM-G998R4 SM-G998A SM-G998P SM-G998T SM-G998U1

Replaces Part Numbers

EB-BG998ABY GH82-24592A EB-BG998ABY=U

Technical Specifications

Voltage3.87V
Amp Hours4900mAh
Capacity4900mAh
Rate18.96Wh
Net Weight63.5g /2.24 oz
Gross Weight88.5g /3.12 oz
Approximate Weight88.5g /3.12 oz
Dimension 69.50 x 64.10 x 6.15mm

Product Highlights

  • Brand: Samsung
  • 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

Why is my Galaxy S21 Ultra showing the wrong battery percentage after I replaced the battery?

The fuel gauge IC was calibrated to the discharge curve of your old cell. Once a new cell goes in, the coulomb counter is working off the wrong baseline — so the percentage reading drifts. Run one complete discharge from 100% down to automatic shutdown, then charge uninterrupted to 100% with fast charging off. After that single cycle, the fuel gauge IC recalibrates to the new cell's curve and the percentage readings stabilise.

Fast charging stopped working after I swapped in the new battery — what's wrong?

On the first cycle after installation, the charge IC sometimes won't negotiate the USB-PD or Samsung Adaptive Fast Charge protocol with a new BMS it hasn't handshaked with yet. This is normal behaviour, not a fault. Charge the phone once at standard speed through a full cycle, then reconnect with your original fast charger. The protocol negotiation succeeds on the second cycle once the BMS has completed one full charge pass.

The phone feels warm near the battery while charging — is that a problem with the new cell?

A new Li-Polymer cell has slightly higher internal impedance than a cell that has been through several charge cycles. Higher impedance means more heat generated during the first few charges — this is expected and not a defect. The warmth should reduce noticeably after three to five full charge cycles as the cell conditions. If it remains hot to the touch after five cycles, check that your charger output does not exceed 45W, which is the rated maximum for this battery.

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