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EB-BG988ABY Samsung Galaxy S20 Ultra Replacement Battery 3.85V 4900mAh

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Fits Samsung Galaxy S20 Ultra with OEM part number EB-BG988ABY.
Voltage is 3.85V at 4900mAh capacity — this matches the original cell and restores full charge cycles.
Connector is flat contact strip; slides vertically into the battery slot with no locking tab.
We ran discharge curves against OEM packs; the BMS voltage held steady under processor and display load.
On first use after installation, disable fast charging for one complete discharge-charge cycle so the fuel gauge IC recalibrates against the new cell's discharge curve before high-current charging resumes.
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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

3.85V

Amp

4900mAh

Samsung Galaxy S20 Ultra — 3.85V Li-Polymer Replacement Battery (EB-BG988ABY)

This is a 3.85V, 4900mAh Li-Polymer replacement battery for the Samsung Galaxy S20 Ultra and Galaxy S20 Ultra 5G. It fits SM-G988Q, SM-G988W, and related SM-G988 variants. It replaces the original EB-BG988ABY cell when the installed battery no longer holds charge through a full day of use.

  • SM-G988 series compatibility: All SM-G988 variants share the same battery bay dimensions, connector pinout, and BMS handshake protocol. Swapping within this series does not require firmware changes or hardware modification.
  • Bench tested on actual hardware: We ran this cell in an SM-G988W and monitored charge acceptance across the full CC/CV curve. The BMS engaged correctly at both 25W and 45W input, and thermal cutoff held within spec at the top of the charge cycle.
  • 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 load into an uncalibrated coulomb counter.

Sudden shutdown at 20–30% after fitting the replacement cell

This happens because the S20 Ultra's fuel gauge IC still holds the discharge curve from the old, degraded cell. When the new cell hits a voltage point the IC misreads as near-empty, the phone cuts power to protect itself. The phone is not faulty and the replacement cell is not faulty. Run one full discharge to below 5%, then charge uninterrupted to 100% without fast charging enabled — the IC recalibrates its low-voltage cutoff threshold against the new curve. After that cycle, shutdowns at 20–30% stop.

USB-PD fast charge not triggering on the first cycle after replacement

After a cell swap, the S20 Ultra's charge IC sometimes falls back to standard 5V input on the first charge cycle. This occurs because the BMS on the new cell has not yet completed its initial handshake with the device's power management IC. Plug in the original Samsung charger, wait for the charge session to complete fully, then unplug and re-plug — fast charging typically resumes from the second cycle onward. If it does not, check that the USB-C port is clean and that the cable supports 45W negotiation.

Compatible Models

Galaxy S20 Ultra Galaxy S20 Ultra 5G SM-G988Q SM-G988W SM-G9880 SM-G988U SM-G988U1 SM-G988N SM-G988B/DS

Replaces Part Numbers

EB-BG988ABY

Technical Specifications

Voltage3.85V
Amp Hours4900mAh
Capacity4900mAh
Rate18.87Wh
Net Weight68g /2.40 oz
Gross Weight93g /3.28 oz
Approximate Weight93g /3.28 oz
Dimension 73.35 x 62.55 x 6.00mm

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

My S20 Ultra shows the battery percentage jumping around erratically after I put in the new cell — is the replacement faulty?

The cell is almost certainly fine. The fuel gauge IC in the S20 Ultra uses a coulomb counter calibrated to the old cell's discharge curve, and that curve no longer matches the new cell. The result is erratic percentage readings until the IC re-learns the new curve. Run one full, uninterrupted discharge down to auto-shutdown, then charge to 100% with fast charging disabled — after that single cycle, the percentage should stabilise.

The phone won't turn on at all after the replacement battery sat in a drawer for a few months before installation — what happened?

Li-Polymer cells self-discharge in storage, and if the cell dropped below approximately 2.5V per cell, the BMS locks out to prevent damage — the phone will show nothing on screen even when plugged in. Connect it to the original Samsung charger and leave it for 30–45 minutes without pressing any buttons. The BMS recovery circuit trickle-charges the cell back above the lockout threshold, after which the phone boots normally. If the screen still shows nothing after an hour, check the charge port for debris before assuming a deeper fault.

The phone feels noticeably warm near the battery area during the first few charges after fitting the replacement — should I stop charging?

Mild warmth on the first few charge cycles is normal with a new high-impedance cell. The charge IC applies full current into a cell whose internal resistance is slightly higher than a worn cell, generating more heat than you may be used to. Keep charging in a ventilated spot and avoid stacking the phone face-down on fabric. If the back becomes hot enough to be uncomfortable to hold, disconnect and let it cool to room temperature before continuing — that level of heat indicates a charge IC issue, not normal break-in behaviour.

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