Key Takeaways
- The Bluetti B300K offers the best value for expanding energy storage.
- It is more compact than previous models for easier stacking.
- The standalone B300K offers a single USB port and no charging.
If you’ve bought a large Bluetti power station but realized it still does not have enough capacity for your needs, don’t worry: you can add more capacity. The Bluetti B300K with 2,764Wh is the cheapest expansion yet at just over 50 cents per Watt-hour of energy storage—and you can get it even cheaper during the launch phase. It strips out a lot of the features found on the previous B300 expansion, but you probably didn’t use them anyway.
Bluetti B300K
$1200 $1500 Save $300
The B300K is a minimalist storage expansion for the Bluetti AC300,AC500, and AC200L or AC200 Max, designed for those who want the best value way to increase their energy storage, with a 4000-cycle lifetime on the LFP cells.
As a standalone battery though, it offers a single USB-A port and no charging capabilities.
- Best value way to add energy storage
- More compact than the B300 so it’s easier to stack
- Up to 4 units can be connected to AC300; 6 to the AC500.
- 4000 cycles lifetime
- A single low-power USB port is insufficient for standalone use
- Can’t be independantly charged
- Requires a different cable to connect to the AC500
Price and Availability
The B300K is available now, at the time of publishing, for a special launch price of $1,200 (43 cents per Wh) until September 23, 2024, with a regular price of $1,500. You’ll also find various bundles when purchased with a matching AC300 inverter. While this makes it incredibly good value, existing AC500 owners might instead consider the B300S, which is also on sale at $1,500, or the equivalent of 48 cents per Watt-hour. While larger, the original B300 and B300S offer independent charging capability, another USB port, and a 12V car socket. The B300 is currently sold out.
AC500 owners should also be aware that they’ll need a different interconnect cable than the one supplied with the B300K; the cable supplied is only for use with the AC300, AC200L, and AC200 Max. The cable alone is an additional $100, which you should factor in.
Design and Comparisons to The B300/B300S
The B300K weighs 29.5kg (65 lbs) and has the same footprint as the AC300 and AC500 Bluetti power stations, allowing it to stack neatly. It can also expand the AC200L/Max, but they have a different footprint, as I’ll discuss later. At 525 × 327 × 209mm (20.67 × 12.87 × 8.23 inches), it’s a fair bit shorter than its B300 predecessor, but the B300K features the same inset handles on either side to help lug it around.
Five green LEDs on the front indicate current charge levels and a soft power button is included. You don’t need to press it because the inverter you have it connected to can power it on or off via the interconnect cable.
On the right-hand side are the two large, proprietary plug sockets for connecting to your main inverter and daisy-chaining these expansions—but how many you can connect together depends on the inverter you’ve connected them to. A single, thick cable is included in the box.
As for design, there are some slight differences in the design language from the B300/S, but the main difference is the color; it’s a lighter shade of gray, and the logo is also lighter, which matches the more recent AC200L but not the older AC300 that sits in my kitchen. First-world problems, indeed.
The main difference between the B300/S and the new B300K is the distinct lack of… everything aside from extra battery capacity. The B300/S featured a 100W USB-C port, an 18W USB-A, a 12V car socket, and a direct charging input for 200W of solar or from an AC plug. While it didn’t offer an AC inverter for output, it had everything else you could possibly need.
The B300K, meanwhile, features a single USB-A port, and even then, it outputs at a slower 12W! There’s no solar input, AC charging, or car socket. That’s it. It almost feels like Bluetti added a single USB port to say, “There you go, it has an output port, now we can call this standalone,” but I can’t imagine any situation where you’d choose to leave the house with a 30kg battery that has a single low-power USB port.
Granted, the entire unit is slimmer and 7kg lighter, but it also has a slightly smaller capacity.
Perhaps Bluetti figured that you already have all the input and output needed on whatever you’re connecting this to, so all those additional ports and charging circuitry were superfluous. I can see the logic in that, but I often find myself using the B300 ports in addition to those on the AC300. The ability to use the B300 standalone as a basic but oversized standalone battery is kind of neat, even if I never actually used it that way.
Of course, Bluetti is passing these cost savings on, making expanding your energy storage cheaper than ever. The B300 (3072Wh for $2,000) works out at $0.65 per Wh of storage, while the B300K, at $1,500 and 2764Wh, is $0.54 per Wh. They’re also not discontinuing the B300/S; both can be used together in the same system.
Testing the B300K
I tried connecting first to the AC200L, which was less than ideal. The footprint is different, so stacking them doesn’t look great, but even more annoyingly, the expansion port is found on the left of the AC200L and on the right of the B300K. To get the short cable to connect when stacking them, you need to turn one or the other around. This isn’t a huge deal as there’s little reason to look at the B300K remaining capacity LEDs, nor to use its paltry single USB port, but it’s a little strange nonetheless.
You can place the B300K side-by-side with the AC200L, but that also looks a little odd with dramatically different heights.
Before plugging into the 2048Wh AC200L, it showed 66% remaining. After plugging in the B300K, which had 71% remaining (I found that out only after connecting it via the smartphone app), it reported a new total capacity of 68%. At first, this seemed a little disconcerting: how could an entire battery pack only add 2% power? But of course, I quickly realized my error: that’s a percentage of the total power remaining, not a percentage of the original power, so it’s averaging the two values. Otherwise, it would be more than 100%.
If the AC200L is 40% and the B300K is 100%, it would show 70% total capacity; the main battery handles any load balancing when charging. Unfortunately, there’s no actual “capacity in Wh remaining” shown on the display, or it would have presumably increased by the respective amount.
Using the Bluetti app (available for iPhone and Android) confirms that it recognizes another battery has been added, and it only takes a few seconds for the inverter display to update with the new capacity.
The B300K suits the larger AC300 and AC500 inverters well, stacking neatly with themselves and the previous B300 (but AC500 owners will need a different cable to the one supplied). The displays also update within seconds of plugging them in, and the on-screen settings correctly report another battery without needing to use the app. When paired with the AC300 or AC500, it can be charged rapidly to 80% capacity in 45 minutes from a household socket.
Neither of these large inverter models have any storage built-in, and must be connected to a battery to function; they handle the DC to AC conversion only. Adding the B300K expansion battery to any of these solar generators doesn’t increase the power output, just the overall capacity. You won’t be able to power any more than you could before, but you will keep it powered for longer. The existing solar input and AC output limits are the same.
Before expanding your system, you might also want to consider whether you’ve maxed out the solar charging capacity. Storage is only one side of the equation; you’ll need to generate more to charge it back up again.
Endless Expansion (Well…33kWh, Anyway)
In terms of how far you can take expansion with the B300K, it’ll depend entirely on the base model you connect to. The AC500 is the largest inverter it’s compatible with, and you can connect up to two chains of three B300Ks to a single AC500. Taking it further, two such systems can be connected together with the help of a Fusion Box, so two AC500 inverters plus twelve B300K expansions gives a total of 33,177.6kWh of storage. That’s enough for an average U.S. household for a day, though the costs are eye-watering, and at that point you would be better served by a purpose-built house battery.
For the more modest AC300, a similar setup with a maximum of eight B300Ks and a Fusion Box nets you 22,118kWh; a single AC300 can support up to four expansions, or 11,059kWh. That’ll service the average UK household.
Lifetime: 4000 Cycles to 80% Capacity
Utilizing LFP (Lithium Iron Phosphate) battery cells, Bluetti claims the B300K will last 4000 cycles (meaning that you drain then recharge it) until it degrades to 80% of the original capacity. LFP cells are usually rated to 3500 cycles, but Bluetti claims to have next-generation cells offering 15% longer life. This isn’t something I can test, as it would be at least a few years before any meaningful degradation is noticed even with daily use, but if true, it’s yet another reason the B300K is great value over its lifetime.
Should You Buy the Bluetti B300K?
Do you need additional storage for your compatible Bluetti power station? If the answer is “yes,” the B300K is the best value option. It’s a no-frills capacity expansion that adds almost zero extra features (except for a token USB port).
If you want a similar expansion that you might actually use by itself at some point, with solar input, a few USB ports, 12V car socket, but no AC output, the B300 or B300S is the better choice. But purely for capacity expansion, the B300K is the best value.
While the B300K can be daisy-chained with multiple inverters, if you need the maximum 33kWh capacity, it’s worth exploring your other options. The Bluetti AC300/500 and B300/S/K are modular, upgradeable, and somewhat portable. They can potentially be used for an entire household, but that’s not the intended purpose, and you’ll get better value from a house battery.
Bluetti B300K
$1200 $1500 Save $300
The B300K is a minimalist storage expansion for the Bluetti AC300,AC500, and AC200L or AC200 Max, designed for those who want the best value way to increase their energy storage, with a 4000-cycle lifetime on the LFP cells.
As a standalone battery though, it offers a single USB-A port and no charging capabilities.
