Adding a Second Battery

Should I add a second solar battery?

Adding a second solar battery: WHEN IT MAKES SENSE: (1) High consumption (5,000+ kWh/yr) — first battery fills up too quickly. (2) EV charging — need more stored solar for evening/overnight EV top-up. (3) Heat pump — winter evening heating needs more stored energy. (4) Smart tariff arbitrage — bigger battery = more profit from Octopus Flux. COST: £3,500-£5,500 for a second 5-10kWh battery. SELF-CONSUMPTION: first battery: 70-80%. Second battery: 85-95%. Diminishing returns — each kWh of extra storage captures less marginal value. ROI: 10-15 years for the second battery (vs 8-12 for the first). COMPATIBILITY: check your inverter supports a second battery. GivEnergy: yes (stacks easily). Tesla: needs a second Powerwall. BYD: modular (add units to existing stack).