Size your off-grid battery bank based on daily energy use, desired days of autonomy, and battery type. Works with lithium LiFePO4 and lead-acid systems.
Depth of discharge (DoD) is how much of a battery's capacity you use before recharging. Lithium LiFePO4 can be safely discharged to 80-90% DoD. Lead-acid batteries should only be discharged to 50% DoD — going deeper significantly shortens their life. This means a 100Ah lead-acid battery only gives you 50 usable Ah, while a 100Ah LiFePO4 gives you 80-90Ah.
Two to three days is standard for most off-grid homesteads in the continental US. This handles typical cloudy weather without running a generator. If you live in a consistently cloudy climate (Pacific Northwest, Great Lakes) or want minimal generator use, size for 4-5 days. Hybrid grid-tied systems can get by with 1 day.
Higher system voltage (48V) is more efficient — it reduces current draw and allows thinner wire for the same power. 48V is recommended for systems over 3 kWh/day. 24V is a solid middle ground for 1-5 kWh/day homestead systems. 12V is only practical for very small systems like a cabin or RV.