One household learned that blackout backup can fail in an unexpected way: despite having solar and home storage, an overnight electric vehicle charging session emptied two Powerwalls before morning.
The grid outage mattered, but the bigger problem was that a large electrical load kept drawing power after the home switched to backup.
Here's what to know
The homeowner said their home installed solar and two Tesla Powerwall 3 units after Hurricane Helene. Then, at about 10 p.m. one night, a drunk driver hit a transformer on the main road near the neighborhood, and the house moved onto battery backup without anyone realizing it.
The original poster said on Reddit in the r/TeslaSolar subreddit, "Need help from keeping ev from charging when grid goes down." The poster said a midnight charging request from a Rivian went through the Wallbox charger and "drained our 2 Powerwall 3 in one hour."
A communications failure also layered onto the battery drain. According to the OP, Wi-Fi went down during the outage, and Wallbox appeared to have lost its NetZero connection, meaning an automation intended to stop charging might not have worked anyway.
A Reddit user suggested, "You can connect your Rivian to Netzero as well. The car has a cellular connection, so it will stop charging more reliably when there is a power outage."
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More background
Even a battery setup that can comfortably cover lighting, refrigeration, and other basic overnight needs can be emptied quickly by one unmanaged high-draw appliance. In many homes, an EV charger is among the biggest electrical loads.
The energy stored in a home battery has practical value, even without assigning a specific cost to one overnight incident. Preserving that reserve can help keep refrigeration, internet access, cooling, and other essentials available, while also reducing the likelihood of needing a gas generator or extra backup equipment.
It also highlights the weakness of outage plans that depend on internet-connected automation. If a router, modem, charger, or cloud platform goes offline at the wrong time, a carefully designed system may no longer behave as intended.
What can be done?
One Redditor said, "My level 2 charger is outside my Powerwall-backed-up circuits on purpose so it does not work if the grid is down. I charge only on level 1 from my solar and batteries if the grid is down."
Some people proposed a hardware-based alternative, such as a contactor or relay that stays energized only when grid power is present, so the charger disconnects automatically during an outage. A local electrician could install that kind of setup.
Another Reddit user said, "I also use Home Assistant and can stop charging my Tesla wall charger from there also when the grid drops. I use pypowerwall for local control of my Powerwall 3's and they are hardwired Ethernet."
Someone else recommended, "For your wifi: consider adding a UPS for your network equipment (modem, wifi access point, etc). During a power outage, there can be a brief loss of power even with Powerwall, and computers are very sensitive to that and will shut down. A UPS will make sure they stay up. Just make sure the UPS can handle a wide frequency range, Eaton units work well."
Where can I learn more?
For a closer look at how home batteries and EVs perform during outages, these stories cover Tesla Powerwall backup, vehicle-to-home systems, and efforts to use EVs as emergency energy resources.
• In California, the whole neighborhood went dark, but a Tesla Powerwall carried the home.
• Tesla's Cybertruck can power your home in an outage, though the setup remains expensive.
• Engineers used EVs to keep the grid operating during a blackout emergency.
• GM unveiled a new game-changing feature that could keep household lights on during outages.
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