How does a lead-acid battery work?
It’s easiest to understand how a lead-acid solar battery works if we break its operation down into two functions: charging and discharging.
Charging
During the day, sunlight hits your solar panels, creating direct current (DC) electricity. This DC electricity travels to a solar charge controller, which regulates the amount of current flowing to the battery to prevent overcharging.
The electricity then flows into the battery, initiating a chemical reaction that stores the energy. The battery's lead plates (electrodes) react with the sulfuric acid electrolyte inside of it, converting lead and sulfuric acid into lead sulfate and producing electrons, which provide the electrical current
Discharging
When you need power later on, such as at night or on cloudy days when your panels aren't actively producing enough electricity to meet your demands, the process is reversed.
The lead sulfate breaks down, returning to its original state of lead, lead oxide and sulfuric acid, which generates electricity you can draw on to power your home (after it passes through your inverter).
» LEARN: How solar energy is stored
Types of lead-acid solar batteries
Lead-acid batteries are typically divided into two main categories: flooded lead-acid (FLA) and sealed lead-acid batteries, also known as valve-regulated lead-acid (VRLA) batteries.
Both types can store solar energy effectively, but they differ in cost, maintenance requirements, lifespan and where they’re best used. Flooded batteries tend to be cheaper but require regular upkeep, while sealed batteries cost more upfront but are easier to maintain.
Flooded lead-acid (FLA) batteries
Flooded lead-acid batteries are the traditional form of lead-acid storage and are commonly used in off-grid solar systems because they’re durable and relatively inexpensive. Inside the battery, lead plates are submerged in a liquid electrolyte solution, which requires periodic monitoring and maintenance.
Because they release gases during charging, FLA batteries must be installed in well-ventilated areas. Owners also need to periodically check electrolyte levels and top them off with distilled water to keep the battery functioning properly.
Sealed lead-acid (VRLA) batteries: AGM and gel
Sealed lead-acid or VRLA batteries are designed to be maintenance-free. Instead of a liquid electrolyte that needs refilling, these batteries keep the electrolyte sealed inside the battery casing.
The two most common types are absorbent glass mat (AGM) and gel batteries.
- AGM batteries use fiberglass mats to hold the electrolyte in place. They charge faster than flooded batteries and are more resistant to vibration, which makes them popular for RVs, small solar systems and backup power applications.
- Gel batteries use a silica-based gel electrolyte. They’re very resistant to deep discharges and temperature fluctuations but generally require more precise charging settings.
Lead-acid solar battery maintenance and safety
Lead-acid solar batteries require regular maintenance and proper safety precautions to operate safely and last as long as possible.
Routine maintenance tasks
Maintaining lead-acid solar batteries mostly involves checking fluid levels, cleaning connections and monitoring overall battery health. Flooded lead-acid batteries require the most attention because their electrolyte levels can drop over time.
Common maintenance tasks include:
- Check fluid levels monthly: The electrolyte should cover the internal plates. If levels are low, top them off with distilled water only, never tap water.
- Inspect battery terminals: Look for corrosion or buildup around the terminals. If present, clean the area with a mixture of baking soda and water and dry thoroughly.
- Tighten connections: Loose cables can reduce efficiency and increase the risk of overheating.
- Perform equalization charges when recommended: Some systems periodically apply a controlled overcharge to balance battery cells and improve performance.
Even sealed lead-acid batteries (AGM and gel) benefit from occasional inspections to ensure connections are secure and charging settings are correct.
Safety and ventilation guidelines
Lead-acid batteries can release hydrogen gas during charging, which is highly flammable if allowed to accumulate. For this reason, proper installation and ventilation are essential.
Follow these safety guidelines:
- Install batteries in a well-ventilated area to prevent gas buildup.
- Keep batteries away from sparks, flames and smoking materials.
- Wear protective gear, such as gloves and safety goggles, when handling batteries or checking electrolyte levels.
- Use insulated tools when working near battery terminals to reduce the risk of short circuits.
If a battery becomes cracked, overheated or severely corroded, remove and replace it immediately. When disposing of old batteries, take them to an approved recycling or hazardous waste facility. Never throw lead and battery acid away with regular household trash.
Lead-acid vs. lithium-ion solar batteries: How do they compare?
If you want to store excess solar energy, your options will likely come down to lead-acid or lithium-ion batteries. The right choice depends on several factors, including your budget, how long you want the battery to last, how much space you have for storage and how much maintenance you're willing to handle.
If you need help deciding, a solar energy company can provide the expertise and experience you need to make the right choice for your home.
Consider your total ownership costs over the battery’s life in addition to the upfront costs.
Pros and cons of lead-acid batteries
Lead-acid batteries are typically more affordable than lithium-ion batteries and produce a lot of power.
However, they have relatively low energy density (meaning they can’t store as much energy in a given amount of space) and need regular maintenance to keep their electrolyte levels correct and prevent sulfation (a buildup of lead sulfate crystals that can reduce the battery's effectiveness).
Pros
- Less expensive upfront
- Well-understood charging mechanism
- Recyclable at the end of their lifespans
- High power output, good for systems with high surge loads
Cons
- Shorter lifespan than lithium-ion batteries (three to seven years)
- Bulkier and heavier for the amount of energy they store
- Require regular maintenance
- Efficiency decreases as they discharge
Pros and cons of lithium-ion batteries
Lithium-ion batteries can last for a decade or longer, making them more cost-effective over the long run despite their higher upfront cost. They’re also more efficient than lead-acid batteries at 95% or more compared to 80% to 85% for their counterparts. However, their high upfront cost can be prohibitive for some.
Pros
- Can last 10 to 15 years
- More efficient at storing and discharging energy
- Require almost no maintenance
- Can withstand more charge/discharge cycles and run low on power without damage
Cons
- Higher upfront cost
- Less established and more complex recycling process
- Fire risk if damaged or improperly charged
» COMPARE: Best solar batteries
Lead-acid solar battery cost
Lead-acid batteries are best for off-grid systems or short-term backup applications where keeping initial costs low is the priority.
Most lead-acid solar batteries cost roughly $100 to $300 per kilowatt-hour (kWh) of storage capacity, depending on the battery type, brand and size. Flooded lead-acid batteries usually fall at the lower end of that range, while sealed versions, like AGM and gel batteries, tend to cost more.
However, lead-acid batteries’ low purchase price can come with higher long-term costs because they usually need to be replaced more often than newer battery technologies.
Upfront costs vs. lifecycle expenses
At first glance, lead-acid batteries can look like the cheapest way to add energy storage to a solar system. However, there are additional costs to consider over time:
- Maintenance: Flooded batteries require periodic watering, inspections and occasional equalization charging.
- Shorter lifespan: Many lead-acid batteries last about three to seven years, depending on how deeply they’re discharged and how well they’re maintained.
- Efficiency losses: Lead-acid batteries generally store and release energy less efficiently than lithium-ion alternatives.
10-year total cost comparison: lead-acid vs. lithium-ion
Although lead-acid batteries are cheaper upfront, their shorter lifespan often requires multiple replacements over a decade of use. Lithium-ion batteries cost more initially but usually last much longer, which can make them more economical over time.
| Battery type | Typical upfront cost per kWh | Approximate lifespan | Replacements over 10 years | Estimated 10-year battery cost |
|---|---|---|---|---|
| Lead-acid | $100 to $300 | 3 to 7 years | 1 to 2 replacements | $2,000 to $9,000 |
| Lithium-ion | $700 to $1,300 | 10 to 15 years | None | $7,000 to $13,000 |
FAQ
Are lead-acid batteries still used?
Lead-acid batteries are still widely used despite the advent of newer battery technologies. They are often employed in applications where cost is a significant factor and where the battery isn’t cycled (charged and discharged) very frequently.
Outside of the solar industry, lead-acid batteries are commonly used in automobiles, backup power supplies, recreational vehicles, marine applications, industrial equipment and mobility aids like wheelchairs and scooters.
How long do lead-acid solar batteries last?
As a rule of thumb, you can expect a lead-acid solar battery to last anywhere from three to seven years, but the lifespan of a lead-acid solar battery can depend on several factors, including the quality of the battery itself, the depth of discharge, the ambient temperature and how well it's maintained.
What’s bad about lead-acid batteries?
While lead-acid batteries have served us well for over a century and continue to be widely used, they do have some drawbacks, including:
- Limited life spans
- Above-average maintenance requirements
- Low energy density
- Possible environmental damage (when improperly disposed of)
- Relatively slow charging
- Declining performance in cold weather
- Worse efficiency than other types of batteries
What is the difference between a deep-cycle battery and a car battery for solar?
A deep-cycle battery is designed to provide a steady amount of power over a long period and can be repeatedly discharged and recharged without major damage. That makes it suitable for solar energy systems, which regularly store and release energy.
A car battery, by contrast, is built to deliver a short burst of power to start an engine and then quickly recharge while the car runs. It isn’t designed for repeated deep discharges, so using a standard car battery for solar storage can shorten its lifespan significantly.
How do you properly maintain lead-acid solar batteries to extend their lifespan?
To extend the life of lead-acid solar batteries, keep them properly charged, avoid deep discharges whenever possible and store them in a cool, dry location with good ventilation. Regularly check the battery terminals for corrosion and make sure connections remain tight.
For flooded lead-acid batteries, you’ll also need to periodically check electrolyte levels and add distilled water when necessary. Following the manufacturer’s recommended charge settings and performing routine inspections can help prevent damage and keep the battery performing efficiently for longer.
Article sources
ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
- 8MSolar, "Lead-Acid vs. Lithium Batteries – Which Is Best for Solar?" Accessed March 12, 2026.
- NAZ Solar Electric, "What Is the Difference in a Flooded Lead-Acid Battery and a Sealed Lead-Acid Battery?" Accessed March 12, 2026.
- SolarQuotes, "Lead Acid Batteries." Accessed March 12, 2026.
- U.S. Department of Energy, "Solar Integration: Solar Energy and Storage Basics." Accessed March 12, 2026.
- U.S. Department of Energy Office of Electricity, "Technology Strategy Assessment: Findings From Storage Innovations 2030: Lead-Acid Batteries." Accessed March 12, 2026.
