LFP / LiFePO4 (Lithium Iron Phosphate)
Lithium iron phosphate battery: 4-5× longer service life than lead-acid, half the weight, no fire risk.
LFP (Lithium Iron Phosphate, LiFePO4) is the safest and most durable lithium chemistry for storage applications. It withstands 3,000-5,000 cycles at 80% DoD (vs 500-700 cycles for lead-acid), weighs half as much and has a very stable voltage during discharge. It does not enter thermal runaway (unlike NMC or LCO used in consumer electronics), making it the standard choice for stationary storage, caravans, marine and as a replacement for deep-cycle lead-acid. Nominal voltage per cell: 3.2 V → a "12 V LFP" battery has 4 cells and delivers 12.8 V nominal (rising to 13.2-13.6 V during charge).
Initial cost 3-4× an equivalent lead-acid, but the cost per cycle is significantly lower. Reference brands: Battle Born, Renogy, Victron Lithium.