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Rover S1 Replacement Battery 3.7V 1500mAh PE2021

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From $27.99 USD $34.99
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Fits Rover S1 and P1 smartphones; replaces OEM part PE2021 and BTR-4100.
3.7V 1500mAh lithium-ion cell delivers full talk time and standby duration on S1.
Connector seats flush into S1 battery slot with positive terminal forward and no locking tab.
We bench-tested this cell in an S1 unit; BMS accepted the pack on first insertion without fault codes.
On first use after installation, disable fast charging for one complete discharge-charge cycle to let the fuel gauge IC recalibrate against the new cell's discharge curve.
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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

1500mAh

Rover S1 / P1 — 3.7V Li-ion 1500mAh Replacement Battery (PE2021 / BTR-4100)

This is a 3.7V Li-ion battery rated at 1500mAh (5.55Wh), built to fit the Rover S1 and P1 smartphones. It replaces OEM part numbers PE2021 and BTR-4100. If your original cell has degraded or failed completely, this is the direct swap.

  • S1 and P1 compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol — one cell covers both platforms without modification.
  • Bench tested on actual hardware: We cycled this cell through charge and discharge on the S1 platform. The BMS accepted the cell on first connect, charge termination triggered correctly at 4.2V, and protection cutoff engaged as expected at the low-voltage threshold.
  • Fuel gauge recalibration on first use: After fitting this cell, disable fast charging for the first complete discharge-charge cycle. This gives the fuel gauge IC time to map the new cell's discharge curve before high-current charging begins on an uncalibrated counter.

Sudden shutdown at 20–30% on the Rover S1 after a cell swap

This happens when the fuel gauge IC is still running the discharge curve of the original, degraded cell. The new cell holds a higher actual voltage at any given percentage, but the gauge reports depletion early because its coulomb counter was calibrated to the old cell. Under modem or screen load, the system sees a voltage that doesn't match its stored curve and shuts down as a protection measure. One full uninterrupted discharge to near-zero, followed by a full charge to 100%, forces the IC to re-anchor its curve to the new cell.

Rover S1 not powering on after the replacement battery sat in storage

Li-ion cells self-discharge over time. If this battery shipped or was stored in a discharged state, the cell voltage may have dropped below 2.5V — the threshold at which the BMS locks out to prevent damage. The phone won't respond to the power button and may show no charge indicator. Connect it to a wall charger, not a USB port, and leave it for 15–20 minutes before attempting to power on. Most BMS circuits will accept a trickle from the charge IC and unlock once the cell climbs back above 3.0V.

Compatible Models

S1 P1

Replaces Part Numbers

PE2021 BTR-4100

Technical Specifications

Voltage3.7V
Amp Hours1500mAh
Capacity1500mAh
Rate5.55Wh
Gross Weight100g /3.53 oz
Approximate Weight100g /3.53 oz

Product Highlights

  • Brand: Rover
  • Manufacturer: CS
  • Series: Standard
  • Color: Grey
  • Product Type: Li-ion
  • Battery Type: Li-ion
  • Warranty: 12 Months
  • Bulk Orders: sales@batteryweb.com

Frequently Asked Questions

My Rover S1 shows 25% battery and then just dies — is the new cell faulty?

The cell is almost certainly fine. This is a fuel gauge IC problem, not a cell defect. The coulomb counter inside the phone calibrated itself to the discharge curve of the old, worn cell — the new cell's voltage at 25% is meaningfully higher, so the gauge trips a protection shutdown before it actually reads empty. Run one full uninterrupted discharge down to automatic power-off, then charge to 100% without interruption. After that cycle, the gauge recalibrates and the shutdowns stop.

Fast charging isn't working on my S1 after I fitted the replacement battery — it's only charging slowly.

On the first cycle after a cell swap, some phones default to standard charge rates until the BMS and charge IC complete a handshake with the new cell. The USB-PD or proprietary fast charge protocol will not engage until the controller trusts the new cell's internal resistance profile. Charge the phone once at the standard rate through a full cycle. On the second charge, fast charging typically resumes. If it doesn't, check that the charger and cable support the S1's required protocol — a standard 5V/1A brick will never trigger fast charge regardless of the cell.

The battery percentage on my Rover S1 jumps around erratically — it was at 60%, then jumped to 80%, then dropped to 45%.

Erratic percentage readings after a cell swap are a fuel gauge recalibration symptom, not a sign of a defective battery. The phone's coulomb counter is interpolating state-of-charge against a curve that no longer matches the new cell's actual chemistry and capacity. The jumps narrow and stabilise after one or two complete discharge-charge cycles. Run the phone down to automatic shutdown, then charge fully to 100% without unplugging early — repeat this twice and the percentage display should settle to within a few percent of actual charge.

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