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Consumer Cellular Envoy U3900 Replacement Battery 3.7V 950mAh

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From $28.99 USD $35.99
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Fits Consumer Cellular Envoy U3900 and replaces the OEM battery.
3.7V, 950mAh lithium-ion cell delivers 3.52Wh to sustain calls and texts on this basic smartphone.
Connector is a standard two-pin JST type; slides into the battery slot with no locking tab.
We bench-tested the new BMS against the Envoy U3900 fuel gauge circuit — the cell accepted a full charge cycle and held voltage under standby load without early cutoff.
On first use, complete one full discharge-charge cycle before relying on the phone's battery percentage display; the fuel gauge IC recalibrates against the new cell's discharge curve during this cycle.
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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

3.7V

Amp

950mAh

Consumer Cellular Envoy U3900 — 3.7V Li-ion Replacement Battery

This is a 3.7V 950mAh (3.52Wh) Li-ion replacement battery for the Consumer Cellular Envoy U3900. The Envoy U3900 is a simplified mobile phone built for seniors and users who want straightforward calls and texts. Swap this in when the original cell can no longer hold a charge or fails to power the device.

  • Envoy U3900 fit: This battery matches the U3900's physical footprint at 53.78 × 34.05 × 4.80mm and connects to the phone's charge IC at 3.7V nominal — the voltage the modem and baseband processor expect under load.
  • Bench tested on actual hardware: We cycled this cell through full discharge and charge sequences on the bench. The BMS held stable cutoff at both ends, and the charge IC accepted the cell without triggering fault flags.
  • Fuel gauge recalibration after swap: On first use after installation, run one complete discharge down to automatic shutdown, then charge to 100% without interruption. This lets the phone's fuel gauge IC map the new cell's actual discharge curve before it starts reporting percentage to the OS.

Why the Envoy U3900 reports the wrong battery percentage after a cell swap

The U3900 tracks charge state using a fuel gauge IC that builds a model of the cell's discharge curve over time. When you install a new cell, that model still reflects the old battery's characteristics — not the new one. The IC reads voltage and maps it to a percentage using stale reference data, so the number on screen can be off by 10–20%. One full discharge-charge cycle gives the IC enough data to rebuild its model against the new cell and report accurately.

Sudden shutdown at 20–30% remaining on the replacement cell

This happens when the fuel gauge IC hasn't finished calibrating to the new cell's voltage curve. Under load — a call connecting, the screen at full brightness — the cell voltage drops sharply at a point the IC still maps to 20–30%. The phone's protection circuit reads that as a valid shutdown threshold and cuts power. Run one complete discharge cycle to let the coulomb counter anchor to the new cell's actual low-voltage cliff, which typically sits near 3.0–3.2V under the U3900's load profile.

Compatible Models

Envoy U3900

Technical Specifications

Voltage3.7V
Amp Hours950mAh
Capacity950mAh
Rate3.52Wh
Net Weight18.7g /0.66 oz
Gross Weight43.7g /1.54 oz
Approximate Weight43.7g /1.54 oz
Dimension 53.78 x 34.05 x 4.80mm

Product Highlights

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

Frequently Asked Questions

My Consumer Cellular Envoy U3900 shows a battery percentage that keeps jumping around after I put in the new battery — is something wrong with it?

Nothing is wrong with the cell itself. The phone's fuel gauge IC is still using calibration data from the old battery and hasn't mapped the new cell's discharge curve yet. The erratic percentage readings are the IC recalculating as it collects voltage samples from the unfamiliar cell. Run one full discharge to automatic shutdown followed by an uninterrupted charge to 100% — the jumping should stop after that cycle.

The Envoy U3900 gets noticeably warm near the battery compartment while charging the new cell — should I be concerned?

A new Li-ion cell typically has slightly higher internal impedance than a well-used one, which causes the charge IC to push slightly more voltage to maintain the target current. That produces more heat at the cell surface during the first few charge cycles. The warmth is within normal range as long as the phone isn't hot to the touch. If it stays warm only during charging and cools down once full, the charge IC is operating correctly — no action needed beyond the first two or three cycles.

The Envoy U3900 won't turn on at all after the replacement battery sat in a drawer for a few weeks before I installed it — what's happening?

If the cell discharged below roughly 2.5V during storage, the BMS will lock out charging as a protection measure against over-discharged lithium cells. Plug the phone into a wall charger — not a USB port — and leave it connected for at least 30–40 minutes before attempting to power on. The charge IC needs sustained low-current trickle input to bring the cell voltage back above the BMS re-enable threshold before normal charging and startup can proceed.

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