5 things I didn’t know about home batteries during our hands-on lab testing
I’ve been writing about home battery systems for over a year, but these large devices are difficult to test in practice. Firstly, they are much larger and more expensive than, for example, a telephone. And you have to install them in your home’s electrical system – not easy when you live in an apartment.
Fortunately, CNET has a testing lab that allows us to get more hands-on experience with these large batteries. In our lab in Louisville, Kentucky, we currently have two home battery systems set up for testing: the Bluetti EP900 (our current pick for the best solar battery) and the Savant Power Storage 20.
After finally taking a look at these systems beyond just the spec sheets and paperwork they come with, I realized that there is a lot more to these systems than meets the eye. Here are just a few things I discovered while playing with these home battery systems.
The switch to emergency power supply takes place almost immediately
The biggest appeal to purchasing a home battery system is that you can power your home during a power outage. But I always wondered how exactly that works. Power outages happen unexpectedly and you don’t want to be in the dark for too long. Fortunately, the switch to backup mode is almost instantaneous.
It happens so fast that you might not even notice the power has gone out as everything goes out within milliseconds. Each battery should have a rated switching time on the spec sheet, usually between 20 and 25 milliseconds. To get an idea of how quickly the switching occurs, we put two batteries, the Savant Power Storage 20 and the Bluetti EP900, through a simulated power outage. The Power Storage 20 has a nominal switching time of less than 70 ms and the EP900 has a nominal switching time of less than 10 ms. You might not think there would be such a big difference in just a few milliseconds, but I felt like there was a noticeable difference.
The Bluetti EP900 definitely shifted faster, but the Power Storage 20 wasn’t far behind. However, neither was continuous. The compressor in the portable AC unit we had turned off during both tests. So technically he was without power for a fraction of a second. If you were to play a game on your PC or console of choice, you would lose all your unsaved progress.
Some batteries can keep themselves warm in colder climates
Most of the home battery features are pretty standard: you have different operating modes, energy tracking and savings, and options to help you manage your utility’s expensive runtime. But the Bluettii EP900 comes with a cool feature that surprised me.
Buried in the app settings is an option to turn “battery heating” on or off. This is essentially a self-heating feature for your batteries. When the battery heater is enabled, the system draws power from the mains to help warm the batteries if the current operating temperature drops below a certain temperature.
Normally, home batteries have the opposite problem: they get so hot that they need internal fans or a cooling system so things don’t overheat. But batteries also don’t perform as well when it gets super cold, so a self-heating feature is nice if you live in a colder climate and plan to install your home battery outside. And while I’m sure other lithium-ion batteries have this functionality, it’s not something that ever makes it into the marketing materials for these systems.
Modular batteries are monitored slightly differently
It’s always great to see more and more manufacturers adopting modular battery designs for their home battery systems. Instead of one large lithium-ion battery, modular systems consist of multiple smaller battery modules connected together. They’re a bit like Lego: you can start small and add more blocks as needed. It’s also much cheaper to start with a small module or two than to buy a giant battery right away.
Modular batteries are also monitored in a slightly different way, with the status of each individual module being monitored separately. This can make diagnosing any problems a lot easier. If something goes wrong with an individual module, you know exactly which module it concerns. And the best part is that the rest of the battery system continues to operate normally. Moreover, replacing a small module is a lot easier than replacing the entire battery system. Non-modular systems tend to shut down completely when they detect battery problems.
However, the individual status of each module is not always displayed in the app. Both systems we tested were modular systems and both apps only displayed the full charge status of the entire system. It doesn’t matter, but if you’re really curious about how your modules are doing, you can usually find some sort of LED lights on the sides of your system. Both the Power Storage 20 and EP900 systems use LED lights to communicate the status of the battery modules. Each module must have its own light. Green means all is well. Any other color probably means a module needs to be charged or something is wrong. I imagine the app also warns you if your system detects problems.
The small green lights indicate the status of each individual module.
Your battery inverter is secretly an energy vampire
Just because your appliances and electronics are turned off doesn’t mean they’ve stopped using power. These are called energy vampires, and they are everywhere in your home, lurking in almost every electrical outlet. And just like the rest of the electronics in your home, your home battery system sucks electricity even when it’s not doing anything.
It’s actually all the inverter’s fault. Your system’s inverter is almost the equivalent of a human brain. Its main job is to convert the stored DC electricity in the battery into AC electricity that your home can use. It also typically houses the system’s communications functions, data collection, and is responsible for detecting mains failures. So yes, that big box on your wall does a lot. Just as humans cannot function without the brain, your home battery system cannot function without the inverter.
And because the inverter is doing so much, it needs a little more juice to flow out. The inverter always consumes power, even in standby mode. The larger the inverter, the more power it needs.
The Savant Power Storage 20 has a gigantic 12.5 kW inverter.
Home batteries are extremely quiet
If you’re concerned about the noise level of home batteries, don’t worry. These systems are not loud (or smelly) like many gas generators. Your home battery is so quiet that you probably forget it exists. Both systems we tested were extremely quiet. The only times we noticed any noise at all was when we were using heavier loads or when the systems were pulling a large amount of power from the grid while charging.
If there is more demand on the inverter, the internal fans are switched on to cool things down. The fans are the only noisy element in these systems, and I wouldn’t even consider it “noisy.” It’s more like a slight buzzing sound. You really shouldn’t be able to hear it from your house. It is much, much quieter than a generator.
