Lead-Acid

Lead-acid batteries are the oldest rechargeable battery technology, invented in 1859, and have been the workhorse of off-grid solar systems for decades. They use lead plates submerged in a sulfuric acid electrolyte to store and release electrical energy through a reversible chemical reaction.

The two main types of lead-acid batteries used in solar applications are flooded (wet cell) and sealed (VRLA — valve-regulated lead-acid, which includes AGM and gel subtypes). Flooded batteries are the cheapest per amp-hour but require regular maintenance including electrolyte level checks and equalization charges. Sealed batteries are maintenance-free but cost more.

Lead-acid batteries should only be discharged to 50% of their rated capacity (50% depth of discharge) to achieve reasonable cycle life. Deeper discharges accelerate plate sulfation and dramatically shorten lifespan. This means a 200Ah lead-acid battery bank provides only about 100Ah of usable energy.

Typical cycle life for a well-maintained flooded lead-acid battery is 300-700 cycles at 50% DoD. AGM batteries achieve 500-800 cycles. In a daily-cycling solar application, this translates to 1-3 years of service before replacement is needed.

While the upfront cost of lead-acid is lower than LiFePO4, the shorter lifespan, limited usable capacity, heavier weight, and maintenance requirements make the total cost of ownership higher over a 10-year period. Lead-acid batteries still make sense for seasonal-use applications, starter batteries, and very tight budgets where upfront cost is the primary constraint.