Lithium Ion technology has made significant advances in the past decade, but Lead Acid Batteries are still the go-to solution for many applications. So the real question to ask is: for my specific application (which in this case is emergency battery backup), what is the best battery to use?

There are commonalities in most solar powered battery backup installations:

The battery bank is only expected to be used during power outages.

This means it most likely won’t be used for more than a few days of the year.

The battery bank can be placed in a location where its size is not particularly important.

Most homeowners have their battery bank in their garage or a storage room.

The battery bank won’t have to be moved.

We help you decide on a location that will not be moved in the foreseeable future.

Let’s get into some differences between Lead Acid batteries and Li-ion Batteries.

The type of lead acid battery preferred for solar electric backup power systems is a Sealed AGM Lead Acid Battery (SLA). These are similar to what’s in your car, but more sophisticated. SLAs are also used in electric wheelchairs and allowed on airplanes. SLAs require virtually no maintenance, if installed properly. As part of a solar electric system, the backup batteries have a lifespan of 10 to 15 years. Because lead acid batteries come from such a well-established industry, over 97% of Lead Acid batteries in the U.S. are recycled. As for manufacturing, 74% of the lead used in manufacturing new lead acid batteries comes from recycling1. The downsides of SLAs include being very heavy and taking up more space than Lithium Ion batteries. For example, a 20 kWh battery bank is 1200 pounds.

Lithium ion (Li-ion) batteries beat out lead acid batteries when it comes to weight and space required. That’s why Tesla vehicles use Li-ion batteries. Where higher energy density is required or weight may be an issue, Li-ion batteries are the clear winner. Examples include Laptops, Mobile phones, and Electric Vehicles. Also, Li-ion batteries have a longer cycle life than SLAs. Cycle life is the number of cycles a cell or battery will undergo before being considered “worn out”2.

Usually, in an emergency battery backup installation, budget dictates the capacity of the battery bank. A lithium ion battery bank of the same energy capacity may be 3 — 5 times the cost of an SLA. There is no cost justification for using Li-ion batteries for backup power because the size and weight of the battery bank don’t matter in a stationary application such as a solar battery backup. Also, because you are unlikely to have a power outage more than 10 times per year, the longer cycle life of a Li-ion battery isn’t a factor either.

“Lead Acid comes out on top as the lowest cost of energy and power output per kilowatt hour.”

— Battery Council International

Until li-ion becomes less cost-prohibitive (maybe after Tesla builds its giga-factory), the go-to solution for backup power will be SLAs.

Find out how much solar electric backup power would cost for your home today.

1. America’s Battery Recyclers