The two main battery chemistries for off-grid solar are lithium iron phosphate (LiFePO4) and lead-acid (AGM or flooded). The right choice depends on budget, depth of discharge and expected lifespan.
Lead-acid should rarely be discharged below 50% — going deeper shortens life sharply. LiFePO4 is routinely used to 80-85% depth of discharge. A 100 Ah lead bank gives ~50 Ah usable; a 100 Ah LiFePO4 bank gives ~85 Ah usable.
LiFePO4 typically lasts several thousand cycles; lead-acid typically far fewer under repeated deep cycling. In a daily-cycled off-grid system, this often makes LiFePO4 cheaper per usable kilowatt-hour over time, despite a higher upfront price.
Cold temperatures reduce available capacity in both chemistries. LiFePO4 charging below freezing must be managed with low-temperature protection; lead-acid is more forgiving in cold charging but loses capacity too.
For daily deep cycling, LiFePO4 usually wins on lifetime cost. For occasional backup use on a tight budget, lead-acid remains a reasonable entry point. Sizing and protection must still be done correctly for either.
Preliminary design information only — final systems must be verified by a licensed electrical contractor.