When you build a tower of some sort, you start with the foundation stone or block.
Except when you’re building a tower of power based on the Bluetti Apex 300 system.
The B300K batteries go UNDER the Apex head unit, thus literally becoming the foundation…
In our series of reviews on the latest and literally greatest of power stations from the House of Bluetti, we focus now on the expansion batteries that extend the capacity of the head unit, the Apex 300.
Please see our previous detailed articles on the capabilities of this system. Or just search “Apex” in the search box above.
If you are considering picking up a Bluetti unit, consider using this link to get an extra 5% off. This works even with their Black Friday specials.
Unboxing and Portability: The B300K’s Weight and Build
Flex your muscles for handling this unit.
At just shy of 30kg, it is best if you move these power houses with 2 people.
Double-boxed, with handles, straps and plenty of foam, the unit arrived safely and without a scratch.
The cable that comes standard in the box is the 90 degree-angled CA90.
These short cables make for very neat connections to the main unit.
This 54Ah unit came to us at 40% charge.
It took a good hour to get it fully charged, keeping in mind that the high charging rate slows down considerably when nearing the 100%…
There are 5 LEDs that show the state of charge in 20% increments.
These lights can also indicate a variety of soft errors or hardware failures.
The exact problem can be found in the User Manual.
Building the Bluetti Apex 300 System: Setup and Scalability
A Bluetti Apex 300 can handle a maximum of 6 expansion batteries. This will give you nearly 20kWh capacity, enough for most homes.
Want more capacity: build another one next to it and so forth.
As for stacking a tower: do not go higher than 5 units. If you have more, just split them up with 3 B300Ks in a stack.
I would, ideally, have 2 Apex 300 units in parallel, each with a couple of B300K batteries, which means you can draw more power simultaneously.
This is important because often you will want to use several heavy power-hungry appliances at the same time, like when cooking, heating or washing.
And this will be the ultimate setup for our home backup system.
B300K Features and Specifications
Here is a quick summary of the specifications of the B300K.
The “300” indicates the unit has a capacity of around 3000Wh.
To be precise: 2764.8Wh.
Expandability with the B300K goes all the way up to 16.5kWh.
The B300K can be connected to the following power stations: Apex 300, AC200L, AC200MAX, AC300, and AC500
The cost per Watt hour is significantly lower than with previous models, thanks to 16% higher energy density.
Fast charging to 80% in 45 minutes.
Useful lifespan with more than 4000 charge/discharge cycles is 10+ years.
Warranty: 3 +1 years.
The Standalone Power Feature: A Small Compromise?
As an expansion battery you would not expect the usual bevy of ports and sockets on this unit.
However, there’s one 12W USB-A port on the front, so you could use the B300K also as a standalone power hub for small personal devices.
I just wonder why Bluetti did not include a USB-C port with some decent output, like 100 or 140W as I only got a measly 8W charge out of it for my phone.
It did not even show the percentage on the app but only that there was a DC output flow and indeed my tablet was charging.
If you do not have the Hub D1, which has all the ports, this would still be useful, even in a tower configuration (see the section on the Hub D1 at the end of this review).
Note: The B300K retains a portion of its energy to prevent overdischarging, which helps protect the battery’s lifespan and ensures long-term performance.
Note: This expansion battery cannot be charged on its own. It needs to be connected to a head unit, like the Apex 300.
TESTING
We have not done much in the way of testing yet for a couple of reasons.
If the capacity has doubled from when we tested the Apex 300, it follows that the runtimes “should” be about double now.
“Should” is the operative word. Of course, actual tests will be done but first we want to install our rooftop solar system.
Preliminary tests did not disappoint our premise: all works as expected.
One thing we also would like to test in the next episode of this series is the bespoke Bluetti Trolley 2.
This sturdy contraption is ideal for small stacks of power units to be wheeled around effortlessly (and safely!) to where the power is needed.
And to trundle the units closer to where your portable solar panels are.
It’ll be a lot safer than what we tried here:
CONCLUSION
The Bluetti B300K Expansion Battery is indeed foundational to building a sufficiently capable backup system for your home.
Whether you want to go totally off the grid, or, like us, you don’t want to be inconvenienced when the power goes out – again – at the most inconvenient time.
It behooves everyone to have some sort of backup system.
Make sure you can provide for any medical needs that demand power, like CPAP machines, and that you still can run your fridge/freezer, some lights and the microwave.
Our advice: do your research and take the first steps.
From our experience, Bluetti can cater to practically any of your power needs.
They have an enviable safety record and a huge range of products.
If you decide on the Apex 300 system, the expansion batteries are just $1999.
DRN readers get an additional discount of 5% by applying the code DRN5.
Check out the B300K on this product page.
Hub D1 – Featuring all the Ports that you wish the Apex 300 had…
Remember the days when you bought an extension box for your laptop that had way more connectivity ports than your laptop?
Well, the Hub D1 is that box for your Apex 300 which only has AC output sockets.
This 700W DC Power Hub has the following 9 output ports:
- 2 x Cigarette Lighter Port
- 2 x 100W USB-C PD 3.0
- 2 x 5V 3A USB-A
- 2 x DC5521 Port
- 1 x 50A Anderson
That Anderson port is extremely handy for vanlife folks and RVers.
Note: an empty Anderson plug is provided so you can rig up your own connector.
First impressions: it is BIG! And bulky with a massive clamp (so you can handily attach it to your Apex 300) and a large plug which goes into one of the extension ports of the batteries or the Apex.
The Apex 300 unit only has one port, so you can’t connect an expansion battery and the DC hub at the same time.
The expansion batteries have 2 ports, and when you have the max (6!) batteries, the D1 hub just plugs into the open expansion port on your last expansion battery.
So, if you wanted to go camping with the Apex, the Hub D1 is an essential add-on because it has the ability to power all your devices you normally take with you.
You can hook up your Starlink, fridge, lights and charge up your laptop and phones.
The puzzling thing that I encountered was that the output Watts reading was only between 20 and 30W when I charged my Galaxy S22 Ultra via USB-C.
I contrasted that with the 50W (!) I get on my Samsung fast charger, rated at 45W, whilst the Hub D1 ports are rated at 100W.
The same with charging my other devices: do not expect fast charging.
Most folks will never reach the 700W draw this device is capable of, but if you do, the Hub D1 is actively cooled for when it is needed.
Cool.
Yes, indeed…
Also neat is that you can switch from 12V to 24V.
And all the various ports are metered on the app, showing voltages and output.
All just for $399.
Check it out here.
Conclusion: Is the B300K the Right Power Backup Solution for You?
If you read this review before the 31st of October 2025: good news, as you can profit handsomely from the Bluetti Black Friday Sale!
Most units are discounted massively.
Here is a prime example: the Apex 300, combined with the B300K expansion battery and the Hub D1 DC Power unit is only 5297 Aussie bucks.
And don’t forget to apply your 5% DRN discount to bring the total price further down!
Check it out here.
As always, DRN thanks Bluetti Australia for allowing us to give our opinion on their power solutions.
