Home Battery System GuideWhen you size a home battery, the first fork is whether to back up the whole house or just the essentials. Whole-home backup keeps every outlet live during an outage. Partial backup powers a chosen set of critical loads. The gap between them is large in both storage needed and cost.
What each approach covers
Whole-home backup keeps normal life running. It stores enough electricity to power your entire house during an outage without changing how you use energy, so every outlet, appliance, and system stays operational.
Partial backup covers only what you pick. Most people choose a few critical loads to power during outages, such as a refrigerator, internet, phone, computer, and some lights, which lets them use a smaller battery.
The difference is scope, not quality. A partial system is a deliberate choice to prioritize the loads that matter most during an outage.
Storage and cost
The capacity gap is the core reason to decide carefully. EnergySage states whole-home systems typically require 30 kilowatt-hours or more of battery storage, roughly equivalent to an average home's daily electricity consumption, while a partial critical-loads setup can get by on about 10 kWh.
Cost follows capacity. EnergySage puts a whole-home system at roughly $33,840 versus about $11,280 for partial backup, making whole-home roughly three times as expensive before incentives.
Those figures explain why partial backup is the common default. Backing only critical loads delivers most of the outage resilience for a fraction of the storage and spend.
Critical load panels and smart panels
Partial backup usually routes through a critical load panel. EnergySage describes it as a secondary electrical panel, separate from your main breaker box, that your battery is wired to feed during an outage, backing up essentials such as a refrigerator, some lights, a phone charger, medical equipment, and an internet router.
The panel exists because of a capacity mismatch. The average U.S. home uses about 30 kWh of electricity per day, but most home batteries store somewhere between 10 and 20 kWh of usable capacity, so limiting the circuits keeps the battery from being overwhelmed.
Smart panels change how those choices are made. A smart load panel provides real-time, app-controlled flexibility over which appliances and circuits receive power during an outage, rather than fixed selections locked in at installation.