I've been writing about home battery systems for over a year, but these large devices are difficult to test in practice. For one thing, they're much bigger and more expensive than, say, a phone. And you have to install them in your home's electrical system – which isn't easy when you live in an apartment.
Fortunately, CNET has a testing lab that allows us to get more hands-on experience with these big 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 best solar battery) and the Savant Power Storage 20.
After finally taking a look at these systems beyond the spec sheets and paperwork that comes with them, I realized that there is a lot more going on with these systems than meets the eye. Here are just a few things I discovered while playing around with these home battery systems.
Switching to reserve power happens almost instantly
The biggest advantage of purchasing a home battery system is being able to keep your home powered during a power outage. But I've always wondered exactly how it works. Power outages happen unexpectedly and you don't want to sit in the dark for too long. Fortunately, switching to backup mode happens almost instantly.
It's so fast that you may not even notice there's been a power outage as everything goes down in a matter of milliseconds. Each battery should come with a nominal switching time on its spec sheet, usually in the range of 20 to 25 milliseconds. To get an idea of how quickly the transition happens, we placed two batteries, the Savant Power Storage 20 and the Bluetti EP900, during a power outage simulation. 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 think there isn't that big of a 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. None of them were seamless, however. The compressor on the portable AC unit we were running shut down during both tests. Then it technically lost power for a split second. If you were playing on your PC or console of choice, you would have lost all unsaved progress.
Some batteries can stay warm in colder climates
Most home battery features are pretty standard—you have multiple operating modes, energy data and savings tracking, and options to help you manage expensive time-of-use fees from your utility. But the Bluettii EP900 comes with an interesting feature that surprised me.
Buried in the app's settings is an option to turn “battery warm-up” on or off. This is essentially a self-heating function for the batteries. When battery heat is on, the system will draw power from the grid to help heat the batteries if the current operating temperature drops below a certain temperature.
Typically, home batteries have the opposite problem: they get so hot that they need internal fans or a cooling system to keep them from overheating. But batteries also don't work very well when they get super cold, so having a self-heating function is nice if you live in a colder climate and plan to install your home's battery outside. And while I'm sure other lithium-ion batteries have this functionality, it's not something that appears in the marketing material for these systems.
Modular batteries are monitored a little differently
It's always good to see more manufacturers adopting modular battery designs for their home battery systems. Instead of one large lithium-ion battery, modular systems are made up of several smaller battery modules connected together. They're like Legos – you can start small and add more blocks as needed. It's also much cheaper to start with one or two small modules than to buy a giant battery right from the start.
Modular batteries are also monitored a little differently, with the status of each individual module being monitored separately. This can make diagnosing any problems much easier. If something goes wrong with an individual module, you'll know exactly which one it is. And the best part is that the rest of the battery system will continue to function normally. Additionally, replacing a small module is much 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 reflected in the application. Both systems we tested were modular, and both applications only displayed the full state of charge of the entire system. It's not a big deal, but if you're really curious about how your modules perform, you can usually find some sort of LED light on the sides of your system. 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 everything is fine. Any other color probably means a module needs to be loaded or something is wrong. I imagine the app will also alert you if your system detects any 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 aren't still consuming energy. These are called energy vampires and they are all over your home, lurking in almost every outlet. And just like the rest of your home's electronics, your home's battery system also sucks electricity, even when it's not doing anything.
In fact, it's all the inverter's fault. Your system's inverter is almost equivalent to a human brain. Its most important task is to convert the DC electricity stored in the battery into AC electricity that your home can use. It typically also houses the system's communication functions, data collection and is responsible for detecting network outages. So yes, that big box on your wall is doing a lot. Just like humans can't function without their brain, your home's battery system can't function without the inverter.
And because the inverter is doing so much, it takes a little more energy to drain. The inverter is always consuming power, even in standby mode. The larger the inverter, the more power it requires.
The Savant Power Storage 20 has a giant 12.5 kW inverter.
Home batteries are extremely quiet
If you're worried about the noise level of home batteries, don't worry. These systems are not noisy (or smelly) like many gas-powered generators. Your home battery is so silent you'll probably forget it exists. Both systems we tested were extremely quiet. In fact, the only times we noticed any sound was when we were running heavier loads or when the systems were pulling a large amount of power from the grid while charging.
If the inverter is experiencing increased demand, its internal fans will turn on to help cool things down. The fans are the only noisy element of 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 this from inside your house. It's much, much quieter than a generator.
