Home Battery Storage: Wiring a Backup Battery System

Home battery storage systems like the Tesla Powerwall, LG Chem RESU, and Enphase IQ Battery have moved from luxury to mainstream. Whether paired with solar or used as a standalone backup power source, these systems require specific wiring that’s distinct from both standard electrical work and generator installation.

Whole-Home vs Partial-Home Backup

Whole-home backup powers every circuit when the grid goes down — requiring a battery system large enough to handle your whole-home load (typically 10+ kWh for even basic usage). Partial backup (critical loads) powers only selected essential circuits (refrigerator, lighting, HVAC, medical equipment) through a critical loads panel. Partial backup uses less battery capacity and is significantly less expensive to install.

How Battery Systems Connect

Most residential battery systems connect between your main electrical panel and either a critical loads subpanel or directly to the main panel (for whole-home backup). The battery’s integrated inverter converts stored DC energy to 240V AC during a grid outage. An automatic transfer switch (built into most modern battery systems) isolates your home from the grid when an outage is detected, preventing backfeed to utility lines.

Wiring a Critical Loads Subpanel

The most common installation approach creates a critical loads subpanel. Selected circuits are moved from the main panel to the critical loads panel. The battery system is connected to the critical loads panel and can power those circuits during an outage while the rest of the house goes dark. The subpanel requires a 60-100 amp feed from the main panel for charging, plus the battery connection output.

Solar Integration

Battery systems paired with solar can charge from solar panels during the day and discharge at night or during outages. Most hybrid inverter systems handle both solar input and battery management in a single unit. The DC coupling approach (panels connected directly to the battery inverter) is more efficient than AC coupling (panels → solar inverter → battery inverter).

Interconnection Requirements

Most utilities require notification or approval for battery systems, especially those designed to operate during grid outages (island mode). Some utilities require anti-islanding protection upgrades. Check with your utility before installing.

Size your backup battery system. Use the Battery Storage Calculator on electricalcalcpro.com to estimate the kWh capacity needed to back up your critical loads.