Should I add a battery (Tesla Powerwall, Enphase) to my solar?

Adding battery storage costs $10,000–$18,000 per battery (Powerwall 3 currently ~$14K installed, Enphase IQ Battery 10 ~$11K). Worth it if (1) your utility has poor net-metering (California NEM 3.0, anyone on time-of-use export rates), (2) you have frequent grid outages (TX, FL, parts of the Northeast), or (3) you want energy independence. Federal 25D covers 30% of battery cost (must be 3+ kWh standalone or paired with solar). Payback period 10–18 years on financial metrics alone, faster if you have monthly grid-outage events that disrupt food storage or remote work.