Best Solar Battery for Home Backup

AC-coupled vs. DC-coupled: what's the difference?

An AC-coupled battery (Enphase IQ Battery 5P, FranklinWH aPower 2, Generac PWRcell 2 in this list) has its own built-in inverter and connects to your home's AC wiring, the same side your solar inverter already feeds into. That makes it straightforward to add to an existing solar system without touching your current inverter — a common choice for retrofits.

A DC-coupled battery (Tesla Powerwall 3, SolarEdge Home Battery 400V here) connects directly to the DC side, before your solar inverter converts anything to AC. That means one fewer DC-to-AC-to-DC round trip when charging the battery straight from your panels, which is marginally more efficient — but it typically requires a specific compatible (often hybrid) inverter, which usually makes it a better fit for a new install than a retrofit onto an existing system.

Round-trip efficiency in the table above already reflects each battery's real losses either way — you don't need to guess which coupling wins on paper efficiency; the number captures it.

Why a battery matters more than it used to

In states that still credit solar exports near the retail rate, a battery is mostly about backup power during an outage. That calculus has shifted in California and other states moving to net billing: under California's NEM 3.0 Net Billing Tariff, exported solar is paid an hourly avoided-cost rate that runs roughly 75% below the old retail-rate credit. Production you don't use yourself — most of it, since a typical solar-only home is generating at midday while it's out at work or school — is now worth dramatically less than it used to be.

A battery changes that by storing midday production for evening use, when a household actually draws most of its power and grid electricity is most expensive. See our California solar page for a real side-by-side of solar-only versus solar+battery payback under NBT.

Best pick by buyer type

• Whole-home backup out of the box: FranklinWH aPower 2 or another whole-home-rated unit in the table — no need to stack multiple units.
• Retrofitting existing solar: an AC-coupled unit (Enphase, FranklinWH, or Generac here) — simpler to add without re-wiring your inverter.
• New install, maximizing efficiency: a DC-coupled unit with a compatible hybrid inverter (Tesla or SolarEdge here).
• Starting small / budget-conscious: a single smaller stackable unit, added to later — check the $/kWh column, not just sticker price, since a cheaper small unit isn't always cheaper per kWh than a larger one.