Choose the battery chemistry
The two common choices are lithium iron phosphate (LiFePO4 or LFP) and lead acid. They differ in usable capacity, life, efficiency, maintenance, cold behaviour and upfront cost.
How
- Usable depth of discharge (DoD): flooded lead acid is usually limited to about 50%, while LFP is commonly used at 80 to 100%.
- Cycle life: one LFP maker rates about 2,500 cycles at 80% DoD and about 5,000 at 50% DoD. Lead acid deep cycle batteries typically last about 5 to 10 years.
- Maintenance: flooded lead acid needs regular water top ups with distilled water and specific gravity checks. LFP needs essentially none but relies on a battery management system (BMS).
- Efficiency: about 92% round trip for LFP against about 80% for average lead acid (one maker's figures), so lead acid needs a bigger array for the same load.
- Temperature: lead acid loses capacity when cold and can freeze when flat. LFP charge limits vary by product: one maker's datasheet allows charging from +5 °C and another from 0 °C, while both allow discharge down to -20 °C. Always use your battery's datasheet.
- Never use car (starting) batteries: they are shallow cycle and are damaged by deep discharge.
- Make sure the battery is certified for stationary energy storage. Examples: UL 9540 in the US; IEC 62619 is the international safety standard for lithium cells and batteries in stationary and other industrial uses.
Safety: Lead acid batteries release hydrogen when charging and contain sulphuric acid. Lithium batteries can release very high fault currents and can burn if damaged or abused. Sandia testing found LFP cells had much milder thermal runaway than high-energy NCA cells, but total heat still scaled with stored energy, so LFP is not risk free. Any lithium battery in thermal runaway, LFP included, gives off a flammable gas mix (UL FSRI tested NCA and LFP gas). See power-26 and power-27.
Sources
- Balance-of-System Equipment Required for Renewable Energy Systems. US Department of Energy, Energy Saver, accessed 2026-11
- Datasheet: 12.8 Volt lithium iron phosphate batteries Smart. Victron Energy, accessed 2026-11
- Everything you need to know to replace a lead-acid battery bank with LFP batteries. Solar Builder, accessed 2026-11
- ESS separation and maximum quantities: 2021 residential requirements. UL Code Authorities, accessed 2026-11
- Evaluating thermal runaway risks in high energy density cells (SAND report, 2019). Sandia National Laboratories (via OSTI), accessed 2026-11
- Datasheet LFeLi-12100L 12.8 V 100 Ah lithium iron phosphate battery. Leoch Battery, accessed 2026-11
- Experiments Investigating Explosion Hazards from Lithium-ion Battery Thermal Runaways in Residential Garages Conclude. UL Solutions Fire Safety Research Institute (FSRI), accessed 2026-11
- IEC 62619 (ed. 1 2017, replaced by ed. 2 2022): Safety requirements for secondary lithium cells and batteries for industrial applications, including stationary. International Electrotechnical Commission (listing via Genorma), accessed 2026-11