Home Battery Storage Installation

The battery market has matured significantly, and the choices are meaningfully different. Treating them as interchangeable is the most expensive mistake in this space. Capacity (kWh) vs. power output (kW): these are two separate specs. A 13.5 kWh battery can store 13.5 kilowatt-hours of energy -- but how fast it can deliver that energy is determined by its continuous power output rating. The Tesla Powerwall 3 is 13.5 kWh at 11.5 kW continuous. The Enphase IQ Battery 5P is 5 kWh at 3.84 kW continuous (you typically stack multiples). Franklin WH 15 is 15 kWh at 10 kW continuous. If you want to run a central AC unit (3--5 kW), a well pump (1--2 kW), and a refrigerator (0.2 kW) simultaneously, you need a battery with at least 6--8 kW of continuous output, not just enough kWh. DC coupling vs. AC coupling: if you already have solar, this is a critical decision. DC-coupled batteries connect between the solar panels and the inverter -- the battery charges directly from DC panel power before conversion. AC-coupled batteries connect on the AC side of the inverter -- solar charges the battery via an additional conversion step. DC coupling is more efficient (one conversion vs. two) but requires either a compatible all-in-one inverter (like Powerwall 3, which has an inverter built in) or a new hybrid inverter that replaces your existing one. AC coupling is compatible with virtually any existing solar system without replacing the solar inverter. Whole-home backup vs. partial-home backup: most batteries do not back up the entire electrical panel by default. They back up a subset of circuits fed by a "backup sub-panel" or "critical loads panel." Circuits that matter during an outage -- refrigerator, internet router, lighting, phone chargers, medical equipment -- go on the backup panel. Air conditioning, electric water heaters, electric dryers, and EV chargers typically do not go on backup (they would drain the battery in minutes to hours). The Powerwall 3 with a Tesla Gateway 2 can do whole-home backup, but this requires a dedicated gateway installation and a more complex electrical setup. Utility approval: some utilities restrict battery systems on net-metered accounts, require specific anti-islanding configurations, or require a separate interconnection amendment. Check with your utility before purchasing. In California, NEM 3.0 made batteries essentially required to make net metering economically sensible -- this is a good example of how utility policy drives battery economics.

Battery systems are heavy and have strict installation clearance requirements. The site assessment determines whether your preferred location is actually feasible before you buy anything. Weight: the Tesla Powerwall 3 weighs 287 lbs. Enphase IQ Battery 5P is 118 lbs per unit (and you may stack 2--4). Franklin WH 15 is 355 lbs. These cannot be mounted on standard drywall with toggle anchors. They require either a concrete block wall, a metal stud wall with appropriate backing, exterior mounting on the building's structure, or a dedicated floor mount. The installation manual specifies the minimum wall construction required -- follow it. Indoor vs. outdoor mounting: most residential batteries are rated for both indoor and outdoor mounting, but with different constraints. Outdoors in direct sun adds heat stress that can reduce cycle life. In a garage, confirm the temperature range -- many batteries specify a maximum operating temperature of 122°F (50°C), which can be reached in an unventilated garage in summer. Some batteries have rated performance ranges that drop outside of 32°F--95°F. Indoor installations in a utility room or basement are thermally optimal. Clearances: every battery has required clearances on all sides -- typically 12--24" on the service side, smaller on other sides. These are in the installation manual and are verified during inspection. Measure your proposed location with clearances factored in before assuming it fits. Sub-panel planning: if you're installing partial-home backup, the installer needs to identify which circuits will move to the backup sub-panel. This requires opening the main panel and mapping which breakers run which loads. The backup sub-panel is typically a 100A or 125A panel mounted adjacent to the main panel, with its feed coming from the battery gateway. The circuits you want backed up are re-routed from the main panel into the backup panel. Permit: every jurisdiction that permits residential electrical work requires a permit for battery storage. The permit application typically requires a single-line diagram showing the battery, gateway, main panel, and backup panel connections; the battery spec sheet; the inverter spec sheet (if solar is involved); and a site plan showing mounting location. Geek Handy pulls the permit as part of every install.

Physical installation of the battery and gateway is where the site assessment pays off -- if you've done the clearance and structural work upfront, the mounting process is straightforward. Mounting hardware: the battery ships with manufacturer-supplied mounting hardware. Follow the template (usually a paper or cardboard guide that ships with the unit) to mark the anchor points. For concrete or masonry walls, use the specified concrete anchors -- lag bolts in drywall are not acceptable. For wood-framed walls, anchors must reach studs or structural backing. Confirm the torque spec for the mounting bolts (not just the electrical connections -- the mounting bolts also have specs). Two-person requirement: the actual lift is not optional as a solo job for batteries above 100 lbs. The wall mount is typically set at a height where the battery hanging point is about 4--5 feet off the ground, and the battery must be lifted and held in position while the latch or bolt is engaged. On heavier units (Powerwall, Franklin), a third person steadying is genuinely helpful. A battery that drops during mounting is a serious safety event -- lithium batteries can vent or catch fire if the casing is damaged by impact. Gateway mounting: the gateway is a wall-mounted electrical enclosure, typically 12"--24" square and a few inches deep. It mounts near the main panel -- most installs position it within 10 feet of the main panel to minimize the large-gauge wire run between them. The gateway contains the automatic transfer switch circuitry and the grid connection management logic. It is a listed electrical panel device and is treated as such for mounting -- it needs to be accessible, labeled, and secured to the wall with appropriate fasteners. Communication cable: the battery connects to the gateway via a proprietary communication cable (typically an Ethernet or RS-485 cable) in addition to the power cables. Route this cable neatly and away from the high-current power cables -- signal interference in a noisy electrical environment can cause communication faults.

This is the step that requires a licensed electrician in virtually every jurisdiction. Here is what the electrical work actually involves so you understand what will happen when a Geek does it. De-energizing the main panel: the main panel must be de-energized for work on the bus. Unlike EV charger installs where only the service entrance lugs remain live, a battery gateway installation often requires work directly adjacent to the main breaker and bus bars. In most cases, this requires a utility meter pull -- a step that the utility performs, not the electrician. Schedule the meter pull in advance; same-day utility service for a meter pull is not reliably available in most markets. Gateway-to-main-panel connection: the gateway connects to the main panel via a dedicated double-pole breaker (typically 100A--200A, depending on the system). This is the circuit that allows the battery to charge from the grid and to sell power back to the grid when configured for export. The wire between the gateway and panel is large gauge -- typically 2 AWG for a 100A connection or 1/0 AWG for a 200A connection. These runs use conduit. Backup sub-panel installation: the backup sub-panel is a new electrical panel mounted adjacent to (or in proximity to) the main panel. Its line-side feed comes from the gateway's backup output -- not from the main panel directly. During normal operation, the gateway passes grid power through to the backup panel's circuits. During an outage, the gateway's ATS (automatic transfer switch) isolates the backup panel from the grid and powers it from the battery. The electrician moves selected circuit breakers from the main panel to the backup panel -- running new wire between the panels as needed. Grounding: the battery system's enclosure, the gateway enclosure, and the backup sub-panel all require grounding connections to the home's grounding electrode system. The battery manufacturer specifies the ground wire size. Do not share grounds between the main panel, the battery, and the backup panel without reviewing the installation manual -- some systems have specific bonding requirements to prevent ground faults. High-voltage DC connections (for DC-coupled systems): if the battery connects on the DC side of the solar system, the DC connections at the battery involve the full string voltage -- potentially 400V+ DC. These must be made with the solar panels covered (block the panels with opaque material -- cardboard works in a pinch) and with insulated tools rated for DC work.

Commissioning is where the hardware becomes a system. Every major battery has a commissioning app -- the gateway connects to your WiFi and you complete the setup through the manufacturer's app. For Tesla, that's the Tesla app. For Enphase, it's the Installer Toolkit app (used during commissioning by the installer) and then Enlighten for ongoing monitoring. For Franklin, it's the FranklinWH app. Backup mode configuration: the system needs to know what to do when the grid goes down. There are typically two decisions: (1) what minimum state of charge to maintain as a backup reserve (e.g., "always keep 20% reserved for outages"), and (2) how quickly to respond to an outage (most ATS systems transfer in under 20ms -- fast enough that most devices don't notice). Self-consumption optimization: if you have solar, the battery can be configured to charge from excess solar production during the day and discharge to cover home loads in the evening -- avoiding grid import at peak rates. This is the configuration where time-of-use (TOU) rate optimization matters most. You tell the system your utility's peak hours, and it charges when power is cheap (solar production or off-peak grid) and discharges when power is expensive (peak hours, evening). Export settings: some utilities permit battery export to the grid (you get paid for power you sell), while others prohibit it. If your system is configured to export battery power and your utility doesn't allow it, you can face a fine or meter disconnection. Verify your utility's export policy and configure the system accordingly. "Solar-only export" (you can export from solar but not from the battery) is a common restriction that most systems support. Monitoring integration: connect the gateway to your WiFi and register the system in the manufacturer's monitoring portal. You should see the home's consumption, solar production, battery state of charge, and grid import/export in real time. Set up alerts for "battery below X%" and "system fault" -- the monitoring portal handles these. For systems with smart panel integration (Tesla Wall Connector, Sense integration), additional configuration may be available to manage load priority during battery discharge.

The final step is the most important one and the one most installers skip: actually test the backup mode before calling the job done. How to simulate an outage: with the gateway system powered up and connected to the grid, locate the main breaker or the dedicated "grid disconnect" breaker on the gateway (many gateways have a labeled test switch for this purpose). Open that breaker. The gateway's ATS should detect the loss of grid voltage within milliseconds and switch to battery-backed mode. You will hear a click (the transfer switch operating). Any clocks that weren't on the backup panel may reset. Everything on the backup sub-panel should continue running without interruption. What to verify during the test: - All loads on the backup sub-panel are powered - No loads on the main panel (non-backup circuits) are energized -- they should be dead during the outage simulation - The gateway app shows "Backup" or "Off-Grid" mode - The battery state of charge is decreasing as expected - Reconnecting the grid (closing the breaker) smoothly returns the system to grid-tied mode without flicker or fault codes Transfer time: most residential ATS systems transfer in under 20ms. Most electronic devices tolerate this without issue. Some older UPS devices, sensitive test equipment, or certain medical devices may not -- if you have critical equipment that cannot tolerate any power interruption, verify the ATS transfer time against the equipment's ride-through spec. Final inspection: the building inspector will review the permit, check the wiring and conduit, verify labeling on all enclosures (the gateway, battery, and sub-panel all require specific NEC labeling), and may test the transfer switch function. Label compliance is the most common reason for a re-inspection -- have all labels applied before calling for inspection. The battery system's main disconnect, the backup sub-panel, and the gateway typically each require specific labels per NEC 706. Documentation: after inspection approval, register the system with the manufacturer for warranty purposes (this is separate from commissioning in the app), file the final permit card, and save all documentation. If you're on net metering with a battery-export configuration, notify your utility that commissioning is complete so they can update your account.