BLUETTI B500K Review: 5kWh Expansion Battery That Transforms Your System (2026)

Already own an Apex 300, AC300, or AC200L? Then you've probably hit the wall: your station handles daily loads fine, but a multi-day outage or a serious home backup scenario exposes the capacity gap. The BLUETTI B500K expansion battery is BLUETTI's answer to that problem: 5,120Wh of LiFePO4 storage per module, stackable to 100kWh, priced at $1,799.

Spec analysis places the B500K as the successor to the B300K, delivering 85% more capacity per unit at a cost-per-Wh ($0.35) that undercuts the previous generation ($0.40). The upgrade math is straightforward. The question is whether that math translates into a compelling buy for your specific setup.

This review covers the full specs, a direct B500K vs B300K comparison, compatible station configurations, real-world runtime calculations, and a clear verdict on who should buy it. Spoiler: it's a strong buy for existing BLUETTI ecosystem owners, with one important caveat.

Quick Specs: What the B500K Numbers Tell You

The B500K is a passive storage module. It has no inverter, no AC output, and no standalone operating capability. It exists entirely to extend the capacity of a compatible BLUETTI station. That context matters before you evaluate the specs.

Capacity analysis confirms 5,120Wh per module with LiFePO4 chemistry, matching the cycle life (3,500+ charges to 80% capacity) BLUETTI uses across its premium lineup. At the current price of $1,799, the cost-per-Wh works out to $0.35, which represents strong value in the modular home storage segment.

Specification	BLUETTI B500K
Battery Capacity	5,120Wh
Battery Chemistry	LiFePO4 (lithium iron phosphate)
Cycle Life	3,500+ cycles to 80% capacity
Price	$1,799 ($2,899 MSRP), $0.35/Wh
Compatible Stations	Apex 300, AC300, AC200L, AC200Max, AC500, B300K, SolarX 4K, Hub D1
Max Scalability	100kWh (18 units + 3 Apex 300 stations)
B500K for Apex 300 SKU	B500K2-UN-GY-SPFUS-00
B500K for AC300/AC200L SKU	B500K1-UN-GY-SPFUS-00

One spec worth highlighting: the B500K official product page lists compatibility with both current and legacy BLUETTI stations. That broad compatibility is a meaningful advantage over earlier expansion modules with more restrictive pairing requirements.

B500K for Apex 300 vs B500K for AC300/AC200L: Which Version?

Two versions exist, and the distinction is purely about the included cable. The B500K for Apex 300 ships with a CA90 connector optimized for the Apex 300's high-speed input port. The B500K for AC300/AC200L includes a P090A cable for the older station architecture. Both deliver identical 5,120Wh of LiFePO4 storage at $1,799.

Version	Cable	Compatible Stations	Price
B500K for Apex 300	CA90	Apex 300, AC500	$1,799
B500K for AC300/AC200L	P090A	AC300, AC200L, AC200Max	$1,799

B500K vs B300K: How Much of an Upgrade?

The B300K was BLUETTI's first high-capacity LiFePO4 expansion module, and it served that role well. The B500K replaces it with a meaningful jump in per-unit storage, from 2,764Wh to 5,120Wh. That's not a minor revision.

For owners already familiar with BLUETTI's expansion ecosystem, the B300K predecessor and full expansion guide provides the baseline for this comparison. Published B300K review and real-world expansion data shows consistent runtimes with the AC300 at moderate load, providing a useful reference point for B500K projections.

The cost-per-Wh comparison is where the B500K makes its strongest case. At $0.35/Wh versus $0.40/Wh for the B300K, you're getting 85% more capacity per module at a lower cost per unit of storage. For owners planning multi-unit configurations, this compounds significantly across the full system build.

One nuance worth noting: the B300K's lower upfront cost ($1,099 vs $1,799) may still make sense for owners with modest expansion goals. If you need one additional module and won't scale further, the B300K delivers adequate storage at a lower entry price. The B500K's advantage compounds as you add units.

Compatible Stations: What Works With the B500K

The B500K was engineered first and foremost for the primary compatible station, the Apex 300, BLUETTI's flagship whole-home unit. However, published compatibility data from BLUETTI indicates a broader list of supported stations than the previous B300K generation.

Full compatibility data, per BLUETTI specifications:

• Apex 300 (CA90 cable version)
• AC300 (P090A cable version)
• AC200L (P090A cable version)
• AC200Max (P090A cable version)
• AC500 (CA90 cable version)
• B300K (mixed configurations via Hub D1)
• SolarX 4K
• Hub D1 (for multi-battery management)

Real-World Capacity: What Can an Apex 300 + B500K Power?

The Apex 300 ships with 3,072Wh of built-in capacity. Add one B500K, and the combined system reaches 8,192Wh. That's a meaningful shift in what's possible during an extended outage.

Runtime calculations based on combined 8,192Wh capacity show the following estimates at typical appliance draw rates. These figures assume 85% efficiency, consistent with LiFePO4 systems at moderate load:

Appliance	Typical Draw	Runtime (8,192Wh system)
Mini-fridge	~60W average	~116 hours
Full-size refrigerator	~150W average	~46 hours
CPAP machine	~30W average	~232 hours (9+ nights)
LED lighting (5 rooms)	~50W	~139 hours
Laptop	~65W	~107 hours
Combined essentials (fridge + lights + CPAP)	~240W	~29 hours

Real-world performance data consistently shows that systems running a combination of critical loads (refrigeration, medical devices, lighting) can sustain 24-36 hours on an 8,192Wh system without recharge. For outages beyond that range, adding solar input to the Apex 300 extends autonomy substantially.

System Builds: How to Scale Your Setup

The B500K's modular architecture, per published BLUETTI specifications, allows stacking to 100kWh across 3 Apex 300 stations and 18 expansion units. In practice, most residential users will operate in the 1-3 battery range. Here's what each configuration delivers:

Configuration	Total Capacity	Add-On Cost	Best For
Apex 300 (base)	3,072Wh	n/a	Everyday backup, short outages
Apex 300 + 1 B500K	8,192Wh	$1,799	24-36 hour whole-home coverage
Apex 300 + 2 B500K	13,312Wh	$3,598	Multi-day backup, resilient homes
Apex 300 + 3 B500K	18,432Wh	$5,397	Off-grid capable, extended autonomy

A compelling configuration pairs the Elite 300 with B500K for whole-home backup, delivering over 8,000Wh of combined capacity for households that need resilient multi-day energy coverage. Homeowners planning resilient whole-home battery backup systems will find the B500K's modular scalability particularly valuable as energy demands fluctuate seasonally.

For AC300 and AC200L owners considering expansion, the B500K for AC300/AC200L version is available at the same $1,799 price point. Owner-reported data for the B500K for AC300/AC200L shows the same capacity and cycle performance as the Apex 300 variant, with the P090A connector as the only practical difference.

Who Should Buy the B500K?

The ideal B500K buyer already owns a compatible BLUETTI station and has hit a capacity ceiling. That's the primary criterion. The B500K doesn't create new use cases: it extends existing ones.

What does “hit a capacity ceiling” look like in practice? It means your Apex 300 or AC300 handles day-to-day power needs but falls short during multi-day outages, extended winter storms, or high-consumption scenarios like running HVAC support alongside refrigeration and medical devices.

Three use cases where the data most strongly supports a B500K purchase: homeowners in regions with frequent multi-day grid outages; households with medically dependent residents requiring continuous power; and off-grid cabin or secondary residence setups where solar recharge supplements stored capacity.

Verdict: Is the B500K Worth $1,799?

Based on specification analysis and owner-reported data, the B500K represents a well-priced expansion option for existing BLUETTI station owners. The $0.35/Wh cost is among the most competitive in the LiFePO4 modular storage category, and the 3,500+ cycle life means the hardware investment amortizes over many years of use.

The limitations are clear: no standalone operation, not portable by design, and the charge management complexity increases with each additional unit added. For users who understand they're buying storage capacity rather than a standalone power station, those limitations are logical rather than problematic.

The upgrade from B300K to B500K is compelling for anyone planning a multi-unit system. For single-module additions, both options are viable, and the choice comes down to budget versus per-unit capacity.

For a broader look at BLUETTI's full lineup and how the B500K fits within the ecosystem, the Bluetti brand overview covers every model tier from entry-level to whole-home.

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Originally published: April 16, 2026