Lithium-ion vs. lead acid batteries: How do they compare?

If you’re considering home energy storage, there are several types of batteries to choose from. In this article, we’ll compare two of the most common battery options paired with solar installations: lithium-ion and lead acid. Other than the different materials that compose each type of battery, their main difference comes in terms of cost and performance. Lead acid batteries tend to be less expensive whereas lithium-ion batteries perform better and are more efficient.

Battery storage is becoming an increasingly popular addition to solar energy systems. Two of the most common battery chemistry types are lithium-ion and lead acid. As their names imply, lithium-ion batteries are made with the metal lithium, while lead-acid batteries are made with lead.

Both batteries work by storing a charge and releasing electrons via electrochemical processes. Lithium-ion batteries work by discharging positive and negative ions from the material lithium between electrodes. Lead acid batteries use a similar process, only a different material.

With these differences in chemistry come differences in performance and cost. While both lithium-ion and lead acid battery options can be effective storage solutions, here’s how they stack up when compared head to head in key categories:

Lithium-ion vs. lead acid batteries: who wins?

In most cases, lithium-ion battery technology is superior to lead-acid due to its reliability and efficiency, among other attributes. However, in cases of small off-grid storage systems that aren’t used regularly, less expensive lead-acid battery options can be preferable.

Lithium-ion and lead acid batteries can both store energy effectively, but each has unique advantages and drawbacks. Here are some important comparison points to consider when deciding on a battery type:

Cost

The one category in which lead acid batteries seemingly outperform lithium-ion options is their cost. A lead acid battery system may cost hundreds or thousands of dollars less than a similarly-sized lithium-ion setup - lithium-ion batteries currently cost anywhere from $5,000 to $15,000 including installation, and this range can go higher or lower depending on the size of system you need.

While lead acid batteries typically have lower purchase and installation costs compared to lithium-ion options, the lifetime value of a lithium-ion battery evens the scales. Below, we’ll outline other important features of each battery type to consider and explain why these factors contribute to an overall higher value for lithium-ion battery systems.

Capacity

A battery’s capacity measures how much energy can be stored (and eventually discharged) by the battery. While capacity numbers vary between battery models and manufacturers, lithium-ion battery technology has been well-proven to have a significantly higher energy density than lead acid batteries. This means more energy can be stored using the same physical space in a lithium-ion battery. Because you can store more energy with lithium-ion technology, you can discharge more energy, thus powering more appliances for longer periods.

Depth of discharge

A battery’s depth of discharge is the percentage of the battery that can be safely drained of energy without damaging the battery. While it is normal to use 85 percent or more of a lithium-ion battery’s total capacity in a single cycle, lead acid batteries should not be discharged past roughly 50 percent, as doing so negatively impacts the battery's lifetime. The superior depth of discharge possible with lithium-ion technology means that lithium-ion batteries have an even higher effective capacity than lead acid options, especially considering the higher energy density in lithium-ion technology mentioned above.

Efficiency

Like solar panel efficiency, battery efficiency is an important metric to consider when comparing different options. Most lithium-ion batteries are 95 percent efficient or more, meaning that 95 percent or more of the energy stored in a lithium-ion battery is actually able to be used. Conversely, lead acid batteries see efficiencies closer to 80 to 85 percent. Higher efficiency batteries charge faster, and similarly to the depth of discharge, improved efficiency means a higher effective battery capacity.

Lifespan

Batteries are also similar to solar panels in that they degrade over time and become less effective as they age. Discharging a battery to power your home or appliances and then recharging it with solar energy or the grid counts as one “cycle.” The numbers vary from study to study, but lithium-ion batteries generally last several times the number of cycles as lead acid batteries, leading to a longer effective lifespan for lithium-ion products.

Lithium-ion: Tesla-Powerwall 2

The Tesla Powerwall 2 is a good all-around solar battery and pairs well with solar panel offerings from the same company. It has a total capacity of 14kWh,100% depth of discharge, and 90% efficiency. Visit the EnergySage Marketplace to get paired with an installer today.

Lead-acid: Sol-Ark (Portable Solar LLC) Partial Charge Carbon Solar Battery PCC-230

This lead-acid battery from Sol-Ark is great for smaller solar applications and is currently the most popular of its kind on the EnergySage Marketplace. It has a total capacity of 2.8 kWh, 50% depth of discharge and 50% efficiency.

If you need a battery backup system, both lead acid and lithium-ion batteries can be effective options. However, it’s usually the right decision to install a lithium-ion battery given the many advantages of the technology - longer lifetime, higher efficiencies, and higher energy density. Lithium-ion batteries are usually more valuable than lead-acid options despite higher upfront costs.

One case where lead-acid batteries may be the better decision is in a scenario with an off-grid solar installation that isn’t used very frequently. For example, keeping a lead-acid battery on a boat or RV as a backup power source that is only used every month or so is a less expensive option than lithium-ion, and due to the lower usage rate, you’ll avoid many of the drawbacks of lead-acid technology, such as their shorter lifespan.

What is the difference between a lithium battery and a lithium-ion battery?

Lithium batteries are designed to be single use due to their primary cell construction, whereas lithium-ion batteries can be recharged to use many times and have secondary cell construction.

What are the disadvantages of lithium-ion batteries?

Lithium-ion batteries have the potential to overheat and aren’t as safe at higher temperatures.

Can I replace a lead acid battery with lithium-ion?

Yes, you can replace a lead acid battery with a lithium-ion battery as long as you add an external charger.

What is the difference between lithium-ion batteries and lead acid batteries?

The difference between lithium-ion and lead acid batteries is the different materials they are made out of. While more expensive, lithium-ion batteries are more efficient and have a higher capacity than lead acid batteries.

With any large purchase like solar and batteries (paired or separately), you want to consider your options. You can sign up on the EnergySage Marketplace to receive turnkey quotes for solar installation from pre-screened local solar installers. If battery storage is something you’re interested in pairing with your system, we recommend adding a note in your account preferences specifying you’re interested in pricing and information about batteries. Even if a solar installer doesn’t install batteries themselves, they can design a solar panel system so that you can add a battery later down the line.