BLUETTI B500K vs. B300K: Choosing the Right Expansion Battery for Your Power Needs

Whether you're preparing for home backup, planning for extended off-grid living, or simply gearing up for your next big adventure, the need for more power is universal. BLUETTI's modular power ecosystem is designed to grow with your energy demands, allowing you to scale your system for any scenario.

Two of the most powerful options for expanding your energy storage are the BLUETTI B300K and B500K expansion batteries. Both offer significant capacity and seamless integration, but they are tailored for different needs. So, which one is the right fit for you? This guide breaks down the key differences to help you make the perfect choice.

At a Glance: B500K vs. B300K Side-by-Side

For a quick overview, this table compares the core specifications of both expansion batteries.

*The B300K comes with a 3-year standard warranty that can be extended by an additional year upon product registration.

Capacity & Energy Storage

The most significant difference between the two batteries is their capacity. The B500K boasts a massive 5,120Wh, making it an ideal choice for serious, high-demand applications. Its larger capacity is perfect for whole-home backup systems, powering a small business during an outage, or sustaining multi-day off-grid power without needing a recharge. With the ability to scale up to an incredible 100 kWh in a larger system, the B500K is built for maximum energy independence.

The B300K offers a substantial 2,764.8Wh, which is a significant upgrade for most users. This capacity is perfectly designed for daily power needs, safeguarding key appliances like a full-size refrigerator, CPAP machine, lights, and WiFi router during an outage, or powering an extended off-grid adventure.

To put this in perspective, here are some estimated runtimes for common appliances:

Runtimes are estimated using the formula: (Wh × 0.85) / Appliance Wattage. Actual performance may vary.

Longevity & Durability

Both batteries use exceptionally safe and long-lasting LiFePO₄ (Lithium Iron Phosphate) chemistry, but their cycle life and internal construction reflect different design philosophies. A "cycle" refers to one full charge and subsequent discharge.

The B300K leads in longevity with over 6,000+ charge cycles before its capacity drops to 80%. This remarkable durability is due to its use of automotive-grade (or EV-grade) LiFePO₄ cells, which are engineered for the rigors of daily charging and discharging. The B300K's robust aluminum casing is designed for the demands of portability, protecting its advanced wireless components from bumps and scrapes on the go.

The B500K is rated for 4,000+ charge cycles and is engineered with a unique "wireless internal frame." In contrast to the B300K's mobile-first design, this internal structure enhances resilience against shocks and vibrations in a more stationary, semi-permanent installation, ensuring it can withstand the rigors of a home or RV setup.

System Compatibility & Integration

Both the B500K and B300K are designed to integrate seamlessly into the BLUETTI ecosystem, allowing you to easily expand the capacity of your existing power station.

Shared Compatibility

Both batteries are compatible with the following BLUETTI power stations:

• Apex 300

• AC200L

• AC200MAX

• AC300

• AC500

Note that a specific P090D to P150D cable is required to connect either the B300K or the B500K with the AC500 power station. This special cable is required to match the high-power connection ports on the AC500, ensuring safe and efficient energy transfer.

Standalone Versatility

This is a key area where the two batteries differ. While both can function independently of a primary power station, their capabilities vary significantly.

Think of the B300K as a grab-and-go power source for your campsite or workshop. It features a built-in USB-A port, allowing you to directly charge essentials like smartphones, tablets, or even run a 12V fan without needing to bring your entire power station. This makes it an excellent, self-contained power hub for smaller needs.

The B500K, on the other hand, is designed as a pure capacity expansion. To use it for direct DC power, it pairs with the Hub D1, turning it into a powerful DC hub for a sophisticated RV or off-grid cabin setup. This modular approach allows you to build a more complex system tailored to your specific DC power requirements.

Apex 300 + Expansion Battery System Estimated Runtime Table

The Apex 300 offers 2,764.8Wh of base capacity and 3,840W of output power. When paired with expansion batteries, your total system capacity and runtime increases dramatically:

Which Expansion Battery Should You Choose?

Your final decision comes down to your primary goals, portability needs, and how you plan to build out your power system.

The B300K is for the Daily Power User & Adventurer.

Choose the BLUETTI B300K if you prioritize maximum cycle life for frequent use, value the convenience of a built-in USB port for direct standalone charging, and need a lighter, more manageable battery that offers greater portability for your adventures.

The B500K is for the Maximum Capacity Planner & Home Backup Builder.

Choose the BLUETTI B500K if your primary goal is achieving the largest possible capacity for serious home backup or multi-day off-grid living. It's the ideal choice if you plan a semi-permanent installation where weight is less of a concern (such as wall-mounted or on a trolley) and you are building a larger ecosystem with components like the Hub D1.

Expand Your Power Today

No matter which path you choose, expanding your energy storage is a powerful step towards energy independence. Both the B300K and B500K offer best-in-class technology to keep your world running.

Ready to upgrade? Explore the official product pages for the BLUETTI B500K and BLUETTI B300K to learn more and build your ultimate power solution. Be sure to check out compatible power stations like the Apex 300 to create a complete and scalable system tailored to your needs.