Laptop Battery for ASUS V4000F/D V4200J/E X509F X412F B21N1818 11.55V 42Wh 3-Cell Li-ion, Compatible with A41N1818, A41N1821, 0B200-03050000, 1-Year Warranty

**Product Overview**
Upgrade or replace your aging laptop battery with this high-performance 11.55V 42Wh 3-cell Li-ion battery, purpose-built for ASUS V4000F, V4000D, V4200J, V4200E, X509F, X412F series laptops. Whether your current battery no longer holds a charge, drains quickly, or causes unexpected shutdowns, this replacement restores your devices portability and productivity.

**Important Voltage Warning**
Please confirm your original battery voltage is ** 11.55V ** before purchasing. Using an incorrect voltage (e. g., 11.1V or 14.8V ) may cause charging issues, system instability, or permanent damage. This battery is NOT compatible with 11.1V or 14.8V models.

**Compatible Models & Part Numbers**
- ASUS Laptop Series: V4000F, V4000D, V4200J, V4200E, X509F, X412F, X412FA, X412FL, X509FA, X509FL
- Replacement Part Numbers: B21N1818, A41N1818, A41N1821, 0B200-03050000
- Also fits: X509FJ, X509FB, X412FJ, X412FB (please verify connector and voltage)

**Specifications Table**
| Parameter | Value |
|-----------|-------|
| Battery Type | Li-ion |
| Voltage | 11.55V |
| Capacity | 42Wh (3700mAh typical) |
| Cells | 3-Cell |
| Color | Black |
| Connector | 4-pin (compatible with original) |
| Weight | Approx. 200g |
| Certification | CE, FCC, RoHS |

**Comparison Table: Old vs New Battery**
| Feature | Old/Failing Battery | This Replacement |
|---------|---------------------|------------------|
| Runtime | <30 minutes or dead | Up to 4-5 hours (typical usage) |
| Charge Retention | Drops quickly | Stable, long-lasting |
| Safety Protection | Degraded | Overcharge/over-discharge/short-circuit protection |
| Warranty | Expired | 1-Year Warranty |

**Installation Tips**
1. Power off your laptop and disconnect the AC adapter.
2. Remove the bottom panel screws (refer to your laptop manual).
3. Gently disconnect the old battery cable and lift it out.
4. Insert the new battery, reconnect the cable, and secure the panel.
5. Charge the battery fully before first use for optimal performance.
6. If the battery is not recognized, check the connector alignment and ensure the voltage matches.

**Package Includes**
- 1 x Replacement Battery (B21N1818 compatible)
- 1 x Installation Guide (basic steps)

**Note**
This is a third-party replacement product, not an original ASUS part. It is fully tested for compatibility and safety. Please verify your laptop model and original battery part number before ordering.