Understanding 1 week backup sizing
Why battery-only week-long backup gets expensive fast
Even a heavily trimmed critical loads list at 400 watts requires roughly 7 batteries to cover a full week with zero recharge assumed. Since batteries are typically the largest cost component in a backup system, this scale of battery-only sizing is rarely the most practical or affordable way to reach a week of autonomy, a cost the quick financing comparison tool in our Financing category can put into concrete terms. This calculator shows the number specifically so it's clear why most real-world week-long plans look different from simple battery scaling.
What actually calls for week-long planning
Wildfire public safety power shutoff events, which can last several days by design, severe hurricane damage that takes utilities a week or more to repair, and remote rural properties with a documented history of slow restoration are the main scenarios where planning for a full week is genuinely warranted rather than excessive, consistent with outage-duration data tracked by the U.S. Energy Information Administration. The wildfire PSPS planning tool addresses the first of these directly.
Why solar and generator combinations make more sense here
Adding daily solar recharge, assuming reasonable sun exposure across the week, or a generator as an additional backstop, both address week-long autonomy far more affordably than scaling battery capacity to cover the entire period with zero outside input, an approach the Department of Energy's inverter basics guide covers as a standard grid-tied-with-battery configuration. A combined system might need only 1 to 2 batteries plus solar recharge, compared to 6 to 10 batteries for a pure battery-only approach at the same duration. The solar recharge sizing tool models this combined approach, and the hybrid inverter sizing calculator in our Inverters & Equipment category covers the inverter needed to support it.
What to do with this number next
Use this battery-only figure as a baseline for comparison, then check the storm season backup planning tool to see how much a combined approach can reduce it. The battery count vs autonomy tool also lets you experiment with different duration and unit size combinations. If this week-long scenario needs to account for EV charging too, the EV charging with generator backup comparison in our Solar + EV Integration category covers that combined planning. The hybrid inverter sizing calculator checks whether your inverter can handle this result.